Galahad's main artifice is her heal on CX, which is... rather problematic, to say the least. Her secondary artifice is her heal reduction, which invalidates the possibility of using heals such as Awakened Shiori. Not that healing would be much use if you can't kill her.
Galahad is immune to MaxHP% DoT.
Heal Reduction, provided by Stage Girl Futaba and Goddess of the Spring Tsukasa, or Brilliance Reduction are both fine mechanics for dealing with her. Alternatively, you could nuke her off the face of the earth with an overwhelming amount of damage.
On the 28th of December 2020, it was revealed that Galahad's unusually high damage to non-space girls and unusually high 'defense' was a product of an error.
This invalidates all Cheer Yachiyo exit evade loop strategies. Awakened Maya nukes should be significantly easier to pull off.
1) Tower Hikari
Those stats and that dexterity buff is absolutely nasty. Paired with heal/brilliance reduction or a damager, many combinations of two to three girls are possible. The most budget version is as seen below (note that Tower would benefit more from a pure critical/damage dealt memoir), which requires Tower to place a mark on Galahad the turn before Maya climaxes. Requires US16 Maya when Tower is US1, compensate accordingly if Tower is higher US.
1) Awakened Girls and Adcha Girl
When Snow White is alive, use her AP down. Both Awakened girls here should be US16. Ensure that Maya and Kuro have AP down when Snow White leaves, such that you have one turn with which to do as much damage as possible. Clean up afterwards as needed.
1) Awakened Maya - One Shot Day
This CR boss is Special type. As a result, Awakened Maya can replace Awakened Tamao from the Cloud Futaba oneshot strategy. However, take note that Snow Galahad's defense is substantially higher than her cloud counterpart, and requires significantly higher unit skill boosts to be able to defeat Galahad with one climax as compared to Tamao. So- no, Ateam is not generous. US21 Stage Girl Nana is strongly recommended. Of the two midrow offensive buffers, Cheerleader Tsukasa is necessary, and if supplemented by Agent Akira, can bring the run to stability. It is possible to replace one non-utility midrow with a US16 Awakened Claudine, whose buffs and unit skill complement Maya's nicely.
Alternatively, use Cheer Yachiyo's exit evasion so as to have Maya use her climax twice, but timing the climaxes is very difficult and reliant on Galahad's cooperation.
Nurse Mei Fan may be used in place of Maya, but requires significantly higher unit skill levels.