No, she's not an evil genius, but let me spin you a yarn.
She's a homeless woman, so she was perhaps raised by a demanding and misogynistic father figure, from whom she learned to act helpless. Then she figured out in high school that acting dumb makes boys like her. She sort of fell into the identity because it was easy -- her family, friends, and society at large fully expected her to be a dumb slut, so it was easy, even for her, to believe she was, plus she liked the attention.
That's a pretty common thread, and people are WAY more complicated than that. I've found people have rich and varied experiences, even dumb ones. That you couldn't glean anything from this girl other than that she was "stupid" maybe says more about you than about her. She has thoughts and feelings that maybe she either can't express in a way you understand, or that she doesn't care to express to someone who is clearly an outsider.
I'm just saying that people surprise me, and I have a hard time believing some girl is just irredeemably "stupid" and that's all there is to know about her.
There are plenty of people who think I'm whatever they think
I tend to think that if she were that crafty she'd probably have found a way off the streets by now. The only people left on the streets are the worst of the worst.
