Emma Blanchard-Nolan is the beloved daughter of very influential people in Farm station, and is 'seduced' by an older guard who emotionally abuses her and tries to bend her to his will, named Arian Jacob. Arian picked a 16 years old because she'd easily manipulated so that he'd eventually get all he wanted, and given that Emma was a sweetheart to people she cared for but also a rule-breaker, naive, and romantic, she was a perfect target.
She's barely 17 when her father finds out and nearly kills him on the spot - she gets in the way, to save her father and to hurt her abuser, and attacks Arian herself, which results in his death by hitting his head against the wall.
Given her social class, their ages, and her parents insisting it was self-defense, as a compromise she's arrested but they already know she'll be pardoned when 18; there is no 'proof' that Arian was hurting her, nor that he attacked first (which is what she says to keep her father safe), so Sky Box for a year it is because "self-defense" can't be used as a justification.
Initially too depressed to do anything for a few weeks, she realizes she's pregnant (implant malfunction) and that is her push to get up. But the guards provoke her into a fight and she's sent to solitary, gaining an even worse reputation. Her anger only grows.
While she initiated the sexual part of their relationship, she won't hesitate bringing up that her pregnancy alone is proof that Arian was a criminal given their age difference and power imbalance. Given that the Ark is dying, even if Abby tells Jaha about the pregnancy there is no time to re-discuss the situation with the whole council, there are other priorities (like sending the kids to Earth) so Emma thinks there was a meeting and that they chose to keep her in isolation, but in reality there was no time.
She's given books about pregnancy and childcare to at least have a chance.
Ark gossip has that she killed a guard who had been abusing her in some way, so that's also all the 100 would know, besides random rumors you can come up with, and they can have their own opinion too.
She's 16 weeks pregnant when sent to Earth, and only her parents, Jaha, and Abby know about it because she's barely showing and is concealing it with baggy clothes. She'll initially keep hiding it from the other criminals because unsure of what will happen next.
She'd try not to make enemies, but still threaten death if anyone tries to take off her wristband because she wants her parents to know she's okay; she's the type to bring Octavia extra comfort food/flowers when she's confined to camp, and later help Murphy because he's alone and she doesn't like it even if he's made a mess. Follows Clarke's lead more even if she agrees with 'whatever the hell we want' at first.
She CAN become a bit cheerful and hopeful, will call people by first name/easily use petnames, and cares for them even if she doesn't want to, but especially at the beginning is also a good-hearted grump who is mostly on her own and needs time or exceptional situations for her natural warmth to show. She's fine with murder/torture to save her people, however she easily empathizes with traumatized ones even if it's unpopular sometimes (see Myrphy after being tortured by the Grounders).
Her field of "expertise" is being athletic (and a good thief thanks to her mother), so she learn about shooting and fighting as much as it's possible in her circumstances, and once baby Henry is born she will pick up hand-to-hand combat again. But she'll do her best to learn how to be a medic too, so that her only skill isn't 'killing people'.
Most characters will find out she's pregnant in season 2 ,given that season 1 only lasted four weeks, but I'm happy to write things going differently (also because she'd likely try to get information about giving birth alone from Bellamy and Octavia and medical knowledge from Clarke, not to mention she'd freak out badly when accidentally infected by Murphy).
She's against all adults when in Camp Jaha/Arkadia because of what they did to her, kinda distrusts Lincoln because he's older than Octavia and that reminds her of her own situation, at least until she can get to know him better. Since I headcanon that Kane wasn't told about her pregnancy (they had bigger worries) he gets more 'benefit of the doubt' than others, once Emma finds out that he didn't actively choose that fate for her.
They can be changed depending on who she's interacting with; these are just so we can have some basic assumptions if you want to write later seasons:
In s1 doesn't believe in peace with the Grounders, doesn't try to hang Murphy. Cooperates even if grumpy and hunts. Terrified of the infection, may tell Clarke she's pregnant. She tries to hold it together when she thinks her parents died after the Ark came down. Isn't near the dropship when the ring of fire at the end of the season happens because she's a good sniper and is far outside. She's 20 weeks pregnant by the end.
In s2-s3 she's in Arkadia/Camp Jaha, goes with Bellamy and the others to find Clarke; she's against giving Finn up but can see that a quick death for him is the only solution, hates Lexa and Pike and thinks it's smarter to find a way to cooperate with Grounders without trusting them, but can't properly join the resistance due to her pregnancy. Her parents, who were at Farm station and came back with Pike, stay out of it for her. She's 23 weeks pregnant at the end of s2 - 35 weeks after the time skip at the beginning of s3.
If we decide to write her trapped in Mount Weather so she can interact with characters there, they aren't extracting her bone marrow because given her pregnancy she'd quickly die, so they are waiting for the baby (to use him too, some day).
Given ALIE's chip by force in Polis around the end of season 3, whereabouts before then are threads-dependent, but after the City of Light is gone she's heartbroken when the pain comes back all at once. 39 weeks pregnant by then.
In s4 Henry is born on Feb 25. She offers to help in Becca's lab and brings the baby to stay at the house, because they are safer there than in Polis; she knows she won't take her mother's place in the bunker (they have similar skills and there aren't enough spots for both), so she volunteers for the nightblood experiment after Emori gets picked for it, but Clarke injects herself anyway. She takes Henry for one last trip later to go save Raven with the others, having decided her parents will raise him.
Not a default but probable: ends up in space with the others unless you don't want to change the original Spacekru (which is fair even if you don't write them), otherwise she's in the bunker too, because Octavia gave her Raven's spot; she focuses on her son Henry and doesn't completely lose herself inside Wonkru thanks to having her entire family there, but she loves Octavia.
In s5-s6: Absolutely against Madi being given the chip because she's Clarke's daughter, will side with Clarke's reaction even if it goes against people she loves and will argue on Clarke's behalf too because she'd do the same for Henry and she'd have made the same genocidal choices. Believes they all did things they should regret. Will trust Echo if her friends tell her to.
[I'm very willing to bend the timeline so she has Henry earlier since the show up until the end of s4 only covers less than six months, we can say the timeskips were longer]
I will write s1-s5, and potentially s6 if we don't have time-travel/portals to other planets or anything that leads to season 7. We could also go AU, assume that Earth wasn't bombed again at the end of s5 or that it regrows faster afterward, and they can stay there and it's the s6 new characters who arrive on their spaceships like Josephine's family; Eden is spreading, and we can focus on the characters re-learning how to live instead. I'm also open to all kinds of AUs where they just get to live and breathe, including no Praimfaya or an easier s5. If Murphy roleplayers want that sort of plot she'd go looking for the City of Light too and get stuck with him. If Abby roleplayers want, I'd be happy to work on fixing that relationship.