Basenjis are pretty rare, so they're not a breed that often turns up in mixes. But it's certainly possible. Some telltale signs might be a curly tail, fused paw pads on her two middle toes (see http://basenji-freunde.com/pfoten_goldsch_bas.JPG), and a wrinkled forehead. (The absence of any of these doesn't indicate non-basenji parentage, either, of course!)
Behavioral giveaways would be aversion to water, yodeling instead of (or in addition to) barking, strong chase instinct, aloofness, and cleaning herself like a cat.
And if you're really interested in getting to the bottom of her genealogy, you can get a DNA kit nowadays for fairly cheap. Some of them even test for genetic illnesses, as well. The Wisdom Panel series used to be considered the most accurate, but that may have changed in the last year or so since I checked.
At any rate, she's a cutie no matter what her parentage is!