You sound like me somewhat.
I would say there's a possibility she is simply trying to communicate her concerns but doesn't know to gently word it, doesn't know what being supportive looks like. If she's saying what you quoted verbatim, then yeah, that's pretty negative and unsupportive. But if you were paraphrasing... maybe she's being supportive in a different way.
Don't gaslight yourself, but maybe you two need to have a talk about this.
Because if this weren't your fiancee, I'd be advising you to leave (internet stranger opinions are important)
everything is going to b o k