I think it sounds like you are on top of things. I think that the medical advice is to "avoid" or "minimize" sun exposure after a treatment - it would be impossible to completely shield our rambunctious little ones from the sun! Having a PWS would become the equivalent of being a vampire! Ha!
I think it is great that you let her get out there and be a kid, at the same time taking all possible precautions to protect her skin. In my opinion, you've struck a perfect balance! Nothing to feel bad about there.
Also, I have heard several people mention using a zinc sun block to put on the PWS, and they say it works well.