Here are your photos.
I do think this is a hemangioma, but keep in mind that I'm the web designer. My opinion means ... well, just that it's my opinion. You should see a specialist as soon as you can.
Where are you located? There might be a good specialist near you and you can go ahead and get in to see one.
Is she four weeks now? Did I add correctly? And was she born on time or early (that does make a difference .. I think they call it gestational age. Sometimes birthmarks won't be there right AT birth, because they were born a bit early, then the birthmarks show up a couple of weeks later. Near the due date. I've heard that over and over around here.)?
Let us know what happens!