Tauriel (the Hobbit)

Before speaking of her feelings towards individuals, I want to point out that she will always clash with Thranduil regardless of what's going on over the simple fact that Tauriel fully believes in living in harmony with other species, letting them in and most importantly attempting to protect them even if their life-spans are a lot shorter than elves' (or maybe because of it) and that's a value she'll never abandon even when it hurts. Isolationism is seen as both selfish and short-sighted by her.

While I can be open to shipping her with Kili if there is chemistry and development during their interactions, I won't write Tauriel as in love with him, because to me they haven't interacted long enough. The events of the movie still go more or less the same, except for mentions of her feeling romantic love, and instead she just speaks of caring, which is still not taken seriously by Thranduil since Kili is a dwarf she just met, or it can be assumed by literally anyone else that she's in love, because you choose what's more entertainining to you.
But her emotions for Kili are still strong because Tauriel hasn't let herself grow closer to her own people for several reasons (with the exception of Legolas, but even then she has to keep emotional distance in one way or another to avoid overstepping) and Kili is the first person she let herself freely care for, which makes losing him even more painful. 

She's moved not only by the wish to protect dwarves (and everyone) from orcs, which in any case was there in the movie, but feeling protective towards Kili in particular, who shared important bits of his past (talking about his mother) with her, and Tauriel bonds with people quickly when they open up.

She never let herself feel or think about her feelings for Legolas because she's not "worthy" and knows his father won't let it happen, but also had let herself believe Legolas had only platonic feelings for her until Thranduil brought up the truth, and there was no time to unpack. You want to keep it platonic? Perfectly fine by me, you want to write a ship where the love triangle is between Legolas, Tauriel, and her idea that he's too above her? Let's go.

I also headcanon that she's an orphan (and in fact talking about mothers is a way to get her attention), something that deeply hurts her even if she doesn't speak much about it to the other elves.

After the events of The Hobbit she refuses to go back to Mirkwood whether her king allows it out of compassion or doesn't, because it doesn't feel like a home anymore, and while she's not actively fighting Thranduil there isn't any lost affection there, she's out to discover more of the world, furious over her grief if Kili is dead, but also trying to decide what she believes in now that she has experienced the events of The Hobbit. 

I'm basing her portrayal on my headcanons and on Evangeline Lilly's thoughts about Tauriel, which felt very true to me:

"She's slightly reckless and totally ruthless and doesn't hesitate to kill." Lilly also describes Tauriel as a nonconformist, explaining that as a result of her relative youth among Elves, she is brash and impulsive, tending to rebel against the established social order of the Elves.

"She's only 600 years old, she's just a baby. So she's a bit more impulsive, and she's a bit more immature. I think she's more easily romanticized by a lot of things." Alluding to Tauriel's pursuit of the dwarves in The Desolation of Smaug after Thranduil closes his kingdom's borders and forbids any interference on the part of Elves in outside affairs, and her refusal to fight alongside him in The Battle of the Five Armies, Lilly explains, "In a very out of character move for an elf, she's broken ranks and disobeyed authority. That's driven from her own conviction about what is right and what is wrong. She feels so much at odds with Thranduil, that she feels the need to defy him. I think that any defiant role that boxes authority is an easy fit for me, because in life I'm a little bit like that."