Blood in my hamster's cage?

[Juliatxoxo]

I had put an toilet paper tube in my (female) hamster's cage a few days ago and today I notice that there is splatters of red (small red dots) and then there is a smear of red that is as big as wide as two fingers (human) and as long as half a fingernail.

I have no idea what could be wrong with her. What could this be? Her fur does not seem wet in the butt area, and her poop is normal...