Coming out to my mum?

Id never do anything by text but the way my mum treats me I feel like I have a I don't give a **** attitude when it comes to telling her things if that makes sense, but I've had a girlfriend now since May and she's a secret to my family and they don't even know I'm gay let alone have a girlfriend. Ok how does this sound as a plan. Tomorrow me and my friend are going out for the day and My mum no doubt will text me where I am and who I'm with. I'm gonna say I'm with hannah, then i'll say oh yeah by the way she's actually my girlfriend. It seems shitty doing it by text but that way she had time to deal with it away from me and I'll be away from her, when. Next see her we can have a normal conversation about it and she can't flip out really, it seems easier giving our relationship situation as it's not a very good one as it's hard to talk to her about things as she just goes off one. I know it's. It very good but that wat its just easier.