Tell her something like "When you get better, I have something I would like us to talk about".

When you approach the subject don't get too emotional or things like it. If what last hurt her is immaturity, show her that you are mature and stable. Talk like adults, tell her exactly what you said in >>1, and see what happens.

Now might be a little too soon, but don't wait too long. You don't want something to happen between you two because she's hurting right now, you want her to consider your offer when she's starting to get better.

Don't blindfold yourself, odds that she accepts and you both happily live ever after aren't that great; but still as >>2 I believe it's worth the shot. And yeah, you'll regret it if you don't.