Why do hamster pee outside of the cage?

I posted a thread last week about my new dwarf hamster and how she's been scratching a lot. I haven't taken her to the vet yet because she seemed to be getting better. Now I'm seeing her doing it again so I went to Petsmart (where I bought her from last week) to see if they knew anything about it or if they would pay for a visit to the vet that they have there (yeah right) Well they gave me a spray for no charge but I'm very wary of using it. For one thing, its not just for hamsters. Its for rabbits, hamsters, gerbils, mice, ect. Rabbits are a lot larger than dwarf hamsters! It also says that its flea and tick spray, not mite spray.

The manager told me to spray it on her and avoid her eyes and nose. Hmm, ok what happens when she washes herself? It says "warning harmful if swallowed" right on the bottle.

A lot of the dwarf hamsters at Petsmart were scratching. I brought that up to the manager but she just got defensive.

I know that there are some people on here that work at vet clinics, so I was wondering if you have any advice about this. Here are the active ingredients:

Pyrethrins 0.06%

Piperonyl Butoxide .60%

Oh, and its called Ultra Care Flea and Tick Spray for Small Animals

by 8in1. I'll probably give my vet a call too and see what she says, although she doesn't like to diagnose over the phone.