Why is this dog shaking?

A stray came up in my yard today, she appears to be young, she shakes non-stop, and wobbles side to side when she walks she can barely keep her balance, if she moves to fast she does a 360 and falls. The only time she does'nt shake is when she is laying down,but when she raises her head it starts to shake. I seen the dog a few days ago on the side of the road and she was doing the same thing so I'm guessing it's not a seizure. I thought about taking her to the vet but I really can't afford that. I fed the dog know she want leave, so if anyone knows what this sounds like let me know. Thanks