Hamster with swollen ear?!

[Hrimfaxi]

We've noticed our hamster seems to have a slightly swollen ear and on closer inspection, seems to be a blood blister. Although it is isn't hugely swollen, it's noticeable when you get a close look.

Their ears are very delicate, but doesn't seem to be bothering her one bit. She's eating, drinking and generally running around like she should be and otherwise in excellent health, but will be keeping a close eye on it.

Any ideas from the PH rodent keeping community as to what could have caused this? Left us a bit stumped.