NTA. You or anyone else shouldn't be held responsible for simple mistakes like misgendering someone, she is the one who made the decision to be a transexual, that doesn't mean everyone on the planet needs to learn her new pronouns and use them.

If shes hurt by someone saying "hey man" she is the one with the problem, these things should be expected when you change your gender, if it was said by purpose and people constantly called her a man or something I would understand how that could be upsetting.

She doesn't deserve your sympathy for this. Its a really stupid thing to be offended by considering what other trans people have to put up with. Some trans people get bullied and berated constantly, someone accidently said hey man and apologised after. She needs to get a grip.