pregnant & need to tell my mom! help?

okay so im 7 weeks pregnant & found out about 2-3 weeks ago. we recently thought I had a miscarriage that my mom did freak out about when I told her I was pregnant. she would talk to me than not for a couple days. she cried all the time & constantly went to the bar to get drunk. she doesn't know im pregnant right now & my other half & I have decided to keep the baby. I am disabled but will be getting tons of help from my other halfs family. my other half & I are 22 & 19. I have my first ob apt January 13th. I really need the help on how do I tell her & what do I say? my other half & I live with her & cannot move out until august because she needs our help making the rent. so if she freaks out, which I know she will, how do I deal with that stress? my grandma & my mother are the only two that don't support it.. everyone else does.