Poor litle kid....ha, it looks like her head may very well take up half her body weight, even more. So how is she able to stand upright? Her torso barely has enough room for her miniscule vital organs, never mind any badly-needed extra muscle.
And yeah, she does have a bit of a weird walk - but when she runs, like when Mac chases her all over the house in "Go Goo Go", it's much,
much more bizarre - her legs and arms move extremely fluidly, as if she doesn't have any bones in her limbs.
Then again, though, she's not the only one dealing with such an issue - Frankie tends to walk casually from time to time (and sometimes when she runs, though only at certain angles) in a way where her legs also move really fluidly, almost like a pair of noodles, very much like Goo.
http://www.fosters-home.com/screengrabs/1/11-0041.jpg
Ack, sorry, that was the only example of it I could find.
Back to Goo though - yeah, I think her cowboy boots DO add some extra height, as can probably be seen most clearly here.
http://www.fosters-home.com/screengrabs/3/37-0033.jpg
But the problem is, we don't know exactly hwo much it adds, and until then, with her oversized head taken in effect, it makes her seem bigger than she probably really is.
http://www.fosters-home.com/screengrabs/4/404-0063.jpg - See? Right here, she and Frankie look as if they're nearly identical in height.