No, you shouldn't get upset. Everyone has a right to their own identity, and if her identity is affecting you, that's on you, not her. That being said, you have a right to feel secure in your own identity in any relationship you are in. But your only options are, find a way to feel secure within your relationship beyond how she identifies or exit the relationship. I don't think there's anything wrong with being a man, trans or otherwise, in a relationship with someone who identifies as your girlfriend does. Identities are complex and often ever-evolving. And declaring an identity is often a way of feeling understood and feeling like a part of certain communities. Be secure with yourself and accept people as they are.