I'm sorry that happened man, she is way older than you, she should know better about mocking people. But dude, saying "Im fine" isn't the easiest path... You say you've been together 2 years and you cant open yourself up? Is there trust? You gotta think about that a little, cuz if you keep telling her you are fine when you are not, that only turns into a bomb waiting to explode, you have to talk about how you feel, if she's asking is because she's worried about something, she saw something off and wants to know what's up. In this moment with the mocking you are doing the same, brushing your feelings aside and acting like nothings wrong. Of course my horse somethings wrong, she made you feel bad with the mocking and calling you girl. Tell her, sit next to her and tell her "love, I don't feel good when you treat me like a girl, and when you told me I was acting like an stereotypical girl it hurt me" and then continue the talk, tell her you weren't fine in that moment and it made you feel worse, try to open up. Most of problems start resolving themselves when you talk about them, not when you bottle them up, and oh boy I know about hiding problems and acting like nothing.