Why Does My Hamster Keep Biting And Scratching Herself, Is That Normal?

It happens when an animal get flea dermatitis. It occurs due to saliva of flea and it ultimately results into skin infection. In this disease an animal scratches, bites and rubs itself. Keep your pet clean and away from other pets. You should immediately consult a vet.

She probably has fleas you can buy flea shampoo in the shop

Dermal parasites like mites, ringworm, or fleas can cause itching and subsequent self-trauma. Animals will sometimes over-groom secondary to stress, pain, or discomfort. Bacterial infections can also lead to skin problems and itching. Have your hamster examined by a veterinarian to solve the problem and relieve your hamster's discomfort.

Maybe I think its because its worried.or doesnt feel good

Fleas

If your hamster smells and itches wash it in warm water in the sink.
Hope I helped!