Words and opinions spoken by others that have negative views towards an individual are only words. It's the decision of whomever they're directed at that allows what is said to have the effectiveness that causes the negative feelings and emotions. There will always be those who don't or care not to understand individualism and will spout ignorance that dehumanizes someone due to the fear that the world they're living in is changing or they have their own gender identity issues that they are in denial about and project their own insecurities onto others so they're not the only one who feels as low as they do. Your partner is going to have to learn how to disregard the hate-speech used to dehumanize them. Allowing it to be effective validates the individuals reason for what they've said and it will never end. If your partner doesn't acknowledge comments that are meant to keep them down and is persistent about it, they power behind the words is nullified. If they can do that, growth and confidence with their individuality will come easy since the focus is on them and their growth, not worrying about what others think and letting themselves be beat down over it. Family and friendship are meaningless if they're the ones causing your partner's distress, if family and friends can't take your partner as they are and be accepting of their life choices, it doesn't matter how close they once were, they're not worth it to be a part of your partner's life. But they have you and your support, and that means everything. I hope your partner is able to overcome the hurtful things inflicted upon them and discovers who they are and the confidence to be comfortable as they are. I'm proud of anyone and hold them in high regards who chooses individuality over socially acceptable conformity.
I personally can't walk down to street without feeling like I have something on my face by the stares and insulting looks on some people's faces, and I live on Capitol Hill in Seattle, and I'm just heavily tattooed with big holes in my face from stretching piercings. My appearance is not at all out of the norm for this area of Seattle but it happens regardless. But I'm the one looking down on them and their small-minded thinking. But I wasn't always as confident as I am now which took years before I got to where I'm at, and I still have underlying insecurities which are projected outwards and become the thoughts and opinions of what I feel others think about me. I can empathize with your partner and the difficulties they're having. It'll get easier with time and learning to become confident and comfortable with themselves no matter what anyone says to bring them down.