I go to a groomer to have my cat shaved in a lion cut, several times a year. Sammie loves it and according to the groomers she is very comfortable the whole time-purring loudly as she often does. After this last shave(a new groomer @ PetsMart) her body hair/fur seems to be getting patchy and noticeably thinner. What would cause this and should I take her to her Vet(also @ PetsMart's Banfield Veterinary Hospital. Should I worry?

Was her hair thinning before she was shaved, or are you just noticing now because she got it cut shorter?

There's a few options my first guess would be the new groomer doesn't know how to use trimmers. Apart from that it could be any number of things: aloplacia, stress, a thyroid problem, and even ringworm (which she could have gotten from the groomer).

Does she have any other symptoms? --> does she eat normally?

I think the best bet is to give the vet a call and get their opinion on if you should bring her in or not. If there are other symptoms I'd say definitely get her checked out, and even if there isn't it can't hurt for them to have a look at her.

A lot of cats shed when they're stressed, and some shed a lot. It's possible that the new groomer just didn't know how to deal with a cat, or the change in person was stressful. If you're worried, and can afford to do so, then it wouldn't hurt to take her in, or at least call.