I agree, definitely mention this to your pediatrician, I've heard something about how this could be misaligned hip bones? But definitely check it out could be fixed with different strategies.
She always sits in a W, very rarely will she sit legs straight out. And more likely, she actually sits on her legs (knees bent on knees, sitting on legs if you know what I mean). She "walks" on her knees a lot too, raises up on her knees and then shuffles herself side to side. Even walking on our hands, she's more likely to step side to side, then actually go forward.
Kinda sounds like she may end up being pigieon toed with her foot turning out. But if its a hip issue may sure when she sits she is sitting with her feet out straight and not in the W position. The W position puts strain on the hips and can form her legs wrong. I have a problem with my 3 year old still sitting like this.
This is very common it comes from the hips, they can put her into special plastic pants that hold the hips straight ask your doctor about this ,once she is older there are inlays in the shoes that help . heres a link to get a better idea http://www.pediatric-orthopedics.com/Top...
You should mention it to her pediatrician, just to be safe. The earlier a problem is found and treated, usually the better the outcome