From my understanding, by definition, hemangiomas ALWAYS involute by the time puberty is finished. Back then, though, there wasn't a lot known about vascular birthmarks at all. But there are different kinds of vascular birthmarks and your friend should see a specialist who is qualified to diagnose different kinds, because they require different treatments.
1. Laser treatment may or may not resolve the problem totally, depending on what kind of birthmark it is and how involved it is.
2. Again, whether it grows a significant amount depends on so many different factors.
3. It is unlikely that she will "pass on" her birthmark to future children. They are not supposed to be hereditary. That said, I do know of families that have more than one child or family member with a vascular birthmark of some sort. There was some research done at one point about placental tissue and birthmark formation that suggested there may be a link, but I'm not sure how that turned out.
Hope your friend is well and if she'd like to get in touch or if VBF can help with any informational resources, please let us know. You do the same, too!