What if that person is actually attracted to men, even though they have had traumatic experiences with a man or a few men? Unlike what morons like Julie Bindel say, you actually can't choose who/what you're attracted to. You can't just decide "oh, I'm a lesbian" now. You either are or you aren't. Even if you're really a bisexual but you decide to just be intimate with women because you've had some bad experiences with men, that's still not healthy and not addressing the problem. You may not realize it, but sexual trauma does not change your sexuality. A heterosexual or bisexual girl/woman who is raped by a man doesn't all of a sudden become a lesbian because of it.
You seem to think there's no escape from PTSD after you've developed it. That's a very dreary defeatist view of things. It's also false.
The truth is that men and penises in of themselves are not dangerous. A trans woman who happens to have a penis is not some hellish threat to you just by existing or because she identifies and lives as a lesbian. Individuals with penises are not "out to get you". Some of your best lovers may end up being a man or a pre-op/non-op trans woman, but you'd never know because you would reject them out of an irrational phobia. You may go out on a night on the town and meet a beautiful, fun, kind, attractive lady who is great to be around and you fancy her. You're having a great time with her, but she admits to you that she has a penis. Despite her being a wonderful, sexy person, you'd reject her simply because of that? How does that make a bit of sense? You may not know what she likes in bed or anything, but just because of the presence of a certain organ, you'll reject her? What's the logic there? It's not like the penis wasn't always there while you were having so much fun with her. It didn't just magically appear, you know. She's still the same person you're having a great time with.