Re:uncertain about treatments
I don't really know that much about port wine stains (even though I have one) because my parents weren't well-informed and therefore I'm not either. I'm trying to research more to see if I should begin to be concerned.
I'm pretty sure you can have birthmarks that aren't port wine stains. I have a brownish one on my upper thigh that isn't. You should probably specifically ask her doctor if they think it's a port wine stain--it sounds like one. You said it turns purple, and port wine stains usually do when the affected person is cold. Mine does.
Everything I've read says that pws don't usually thicken or cause any other medical problems until the person is in their 30's or above.
As I said before, I don't really know that much, so all I am going to suggest is that you maybe research port wine stains online and make an appointment with a dermatologist to get an opinion about it. They're better when treated earlier, and better safe than sorry, right? Sorry I couldn't help you more.