“My girlfriend is trans and she struggles a lot recently with being comfortable with her body. She hasn't had bottom surgery. I frequently reinforce that I find her attractive as she is and it makes her no less a woman, but it has been weighing heavily on her. She won't be able to do anything about it for at least a few years and it pains me that she can't feel like she is who she wants to be over it. I wish I could help her more, but I don't know how.”
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Someone answered with kindness...
Reaffirming her that she is a woman in your eyes and that you love her and your body is the most important thing you can do.
There probably isn't much more you can do, I think.
Maybe you want to ask her if there is anything that would help her not think about it so much, or something you could change.
But in the end, sorry as I am to say it, it's going to be one of these types of shitty situations that you will have to deal with and endure, there's no miracle cure for it.