When they are capable of interbreeding to produce a viable/ fertile off-springs.
Answer:
Transphobia is a big one of course, but if she's family oriented, not being able to have a pregnancy and children of her own are a huge hit to the self esteem. I've also heard that the scarring from surgeries and dysphoria can make it unbearable at some points.
Explanation:
I have several trans friends, so it's always nice to spread information about these things when I can :)
Night vision because the creature will be able to hunt food in the night, having enhanced eye sight. To continue, light colored fur would make the creature stand out taking away cover and the other answers have no benefit to the scavenger.