i need some advice (my friend just became a mom!)

ok i need some help my friend is 13 and she's been going out with a 17 year old for about 3 months. Well one night when she was at her dad's house it was VERY late and she wanted to go meet her bf who lives in the same apartment complex. Well when she got to his floor she got mugged and her boyfriend's mom heard them and chased them off. well when she told her parents she got mugged they wanted her to go get a pregnancy test because they didn't belive that she wasn't pregnant... so she took the test but it turns out she is but w/ her bf's kid and she's about 2 1/2 months along.

We heard on friday and that same day a girl we thought was our friend spread it out to the whole school. but now she's feeling better about it and me and we're all talking about if its a boy to give it a mohawk and all.

but the thing is my mom doesn't know and since i've been a new kid for about 2 months she probably wouldn't like the idea of my being friends w/ a girl thats already a mom. how do i break it to her so she doesn't hate my friends???
i was thinking about doing it in a public place just so she can't freak out... but i need some advice!!!!!!!!!!!!