I have a pws on my entire left arm and hand that extends to a small area around my heart. There is slight swelling in the area but it is most noticable on my hand. The only discomfort I get is when I get cold or when I am doing strenuous exersize. When I am cold it does "ache" a little and it gets very dark purple. When I am doing accelerated heart rate exersizes I can't have anything around my wrist because it swells and goes numb.
Be sure to let your daughter know how lucky and unique she is. She will get teased about it I am sure but if you have the right attitude and support for her she will be fine. I seriously love having my birthmark where it is. I am physically fit and have a couple of tattoos that use white ink to make the designs etc. Kids ask about it all the time when I am at the pool etc and I just tell them that I am an X-man and have to keep it a secret...sounds goofy but then they leave me alone...lol.
Let me know if you have any questions etc!