Hamsters can get fatty tissue lumps which aren't in themselves dangerous. I know, you're probably worried about cancer, but not all lumps instantly mean cancer.
It's also possible the wee one bumped herself and did herself a small injury.
You should take her in to get her checked just to be sure. If you do, be sure the vet is an exotics specialist.
That's great, thanks for the advice, will take her this weekend when i'm off work.