Re: what kind of doctor for diagnosis
I am 23 with PWS.
I would suggest doing both go to the plastic surgeon that her ped recommended. If he/she tell you to wait and see then find a VAS. What state do you live in? Some one on this site might know another doctor that is not on the list that might be able to help you. Also, someone else might have used the plastic surgeon that was recommended to you and they would be able to tell you if he/she was worth see.
To answer your other question. Yes, if you push on PWS it turns white because you pushed the blood out of the area and then it fills back up. Though I believe there are other kinds of birthmarks that do that as well but not sure. The Plastic surgeon should be able to tell you what type of birthmark you are dealing with. Or, if you want you can either post a picture on this topic by clicking additional options when posting a message, or you can send a picture and ask the PWS expert at the front of this website if your daughters condition is PWS.
I hope this helps and am sure others will chime in later.