Okay so this is a topic that’s sensitive for a lot of people which is understandable because of the way many trans people are treated. But I don’t think it’s alright to call op selfish or just correct her on every social faux pas and tell her to get over herself.
In reality this must have been a huge shock to you OP. The person you’ve been building a relationship with just told you something she knew would change the nature of your relationship. If you were just friends this would be a totally different ball game, but you aren’t. In romantic relationships the sexuality and gender of both people matter. If one of those elements changes for one person and it doesn’t line up with the other person’s, it means that the relationship is over.
It’s understandable why your former boyfriend didn’t lead with the fact that she was planning on transitioning, it’s a big change for a person to go through and some people are horrible and intolerant in secret.
But I don’t think you’re intolerant, any big change in a SO’s life also affects the person they’re in a relationship with and it takes both people time to come to terms with things. The person before that gave some ridiculous example of how if your SO suddenly became disabled you should just accept things is wrong. Caregiver fatigue is very real, needing to take care of an SO in that way isn’t something everyone can or is wrong for not wanting to devote the rest of their lives to. And even if you plan to stay with someone with a new disability, it still takes time to process the change.
You should definitely see a therapist, to come to terms with you pasts relationships and you accept and mourn the end of your current one. Hopefully with a few of the usual breakup cures + some time you’ll be feeling okay again. But probably don’t continue the relationship, the puzzle pieces just don’t fit and denial doesn’t work forever. Right now feelings are running high for the both of you so maybe a little while later you guys could get together for a talk and you could tell her what you meant a bit more clearly, that you don’t think she’s a bad person, you wish her the best, but you needed time to process everything and come to terms with everything.
I hope everything works out good for the both of you guys.