One thing you'll learn is never listen to the pet shops. Often their knowledge is out of date and quite frankly, wrong. Not to worry though, we can guide you in the right direction
What type of wheel do you have? Is it possible that the long hair has got tangled up and pulled? As Jo says, Syrians need a 28cm (11") wheel and even then some require a 33cm (12"). Generally rule of thumb is if the backs bending and not straight, wheel is too small. A wheel in the cage isn't optional, it's compulsory. Hamsters can run up to 5 miles a night.
Personally if you're thinking of hamster ball, it's way too soon. Settling in period where you don't touch her can be anywhere from 3 days to a week. Then start taming her which will take several more weeks. Realistically it could take a couple of months before she's tame and happy to be picked up. That being said some take longer and some not as long. My robo Niko was tame within a month. My Syrian ghost I've had for a month and he's only just got to the stage where he's happy to be out of the cage and handled. What I'm trying to say it don't get a ball yet as it'll be guaranteed that it'll be too small before you get to use it.
Also, hamster ball IS optional. You don't have to have one. Some people prefer using playpens so they free roam. If you decide to use a ball most pet shops stock 18cm balls which are too small for Syrians. By the time they're 5-6 months they are fully grown and will use a 25cm ball marketed for rats.