I don't know that anyone can really tell you that for sure. You know the nature of vascular birthmarks ... they behave the way they behave.
Why don't you ask one of the experts? http://birthmark.org/experts.php
Or see if your doctor's office has an email system and you could email there and ask.
My *opinion* is that you ARE doing the best thing long term, no matter what the birthmark does. If she doesn't want another treatment right now, then ... oh well. Children have so little control. We tell them what to eat, wear, where to go. It might be more of an esteem boost to let her *make* this decision, even if it meant an extra laser treatment as a teen.
PS... and how are you???