How to come out

Hi everyone.

I (22F) been dating a girl for the last 7 months and although its nothing serious we do spend quite a lot of time together which we both enjoy. The thing is I live with my mother who is a little nosey and always asks where I'm going, besides she doesnt know I'm a lesbian. I've known I like girls since I was 17 and it feels like its time to stop hiding both myself and the girl I'm seeing but I just don't how to come out to her. For a little context my extended family (uncles, grandma, aunts, etc) are very homophobic and while I don't think my mother is like them, she does sometimes say things that make me second guess. I know I wont be in danger if I tell her but I'm not sure how she will react.