I think you should mention it again when the time is right. I"m 20 years old and this is my first pregnancy and it was VERY hard for me to tell my parents and my boyfriends parents because of a situation that i'd rather leave out.
But after everything it's brought our families closer and it makes me appreciate life. i know some people frown upon young people have babies so soon, but i've been with my boyfriend for 6 years and he hasn't left me and he won't.
I think she'll realize if she is pregnant, the baby will bring her a lot of joy, I know it has brought me a lot of joy (and stress as well) and it's all worth it