A hemangioma would be visible at birth. It's conceivable that this is a flat hemangioma that becomes more visible when your child is hot, wet, etc., but it'd hard for me to imagine that you wouldn't have noticed it before. In any case, flat hemangiomas don't grow, bleed, or some other unpleasant things. The redness may be mild eczema or a rash of some sort. I agree that another doctor's visit makes sense, but I doubt you have anything to worry about.
Take care.
Dr. Rockoff
However, this new occurence does come mostly when she's hot, back from recess, etc,. But it was never noticeable before about 2 months ago.
Kinda sounds like a flat hemangioma, but was worried it was something more worrisome and possibly lymphatic such as clta.
Dr. Rockoff