Dogs have natural itches, just like sometimes your head itches, but that doesn't mean you have lice, nor your dog has fleas.

If you have searched for fleas, and not found any (granted you did a THOROUGH pick through of the hair) than I doubt she has 'em.

Go get the flea shampoo, give her a couple baths in it, you'll often notice black dandruff stuff, that is flea feces (poop), and fleas are about the size of a small mosquito, they are big enough to see with the naked human eye, so if she gets overridden with fleas, you'd be able to see them.

It's unfortunate that you took this dog under your wing, and now can't face the consequences of that, but it's best to get her into a fabulous home while she's young, as opposed to dumping her off at the pound when she's older. If you don't think you can take care of this dog, petition your parents for help, or give her away, or sell her for a minimal fee.

And next time you get a pet, think twice.