DNA test HELP!

Lisa • I`m strong because I have to be.
Okay sooooooo this girl who is trying to say my boyfriend got her pregnant... She finally had her baby and i want him to get a DNA test to see if it's really his  but don't know how to go about that... Because I'm almost sure she's not going to want to do so since she told me her self she didn't want to get one done! Does anyone have any advice on what to do?? Or how to go about making her get one done, I have a child with this man and I'll be damned if it is his child and he's not there for that child like he is with mine. 
Sincerely freaking out!!