Well, to me being trans is about being unhappy because your body doesn't fit your gender identity or at least being happier when your body is more in-line with your gender identity. That has nothing to do with the gender identity itself, only with the feeling of being in the wrong body (aka dysphoria).
For example, my gender identity doesn't match my assigned sex (I'm agender or gendervoid or something - basically I don't see the point in having a gender) but I don't consider myself trans because I'm alright with my body.
But if you feel those things and you are unhappy with your body than you can absolutely be trans - especially when you're non-binary. At some point bodies will just not match a non-binary gender identity because hormones. And that can absolutely trigger dysphoria. So, if you feel that way you can definitely say you're trans. Maybe you can talk to her about it this way and she might understand.
Hope everything goes well and I wish you all the best! ♥️
