It could be nothing, and it's just the way she likes to walk, or it could be a result of the ligaments in her legs being stretch the wrong way.
When she sits on the floor, does she sit cross legged/ legs out in front, or on her knees with her calves splayed out to the side?
If she continually sits on her knees, it can make it difficult for her to walk with her feet flat.
My niece has this same problem.
A Dr should be able to tell quickly if it's the latter.
Being so young, it's no big deal and can easily be corrected by encouraging her to sit differently.