What sort of activities has she been doing lately? Some girls get a small bleed when they tear their hymen - sports, horseriding etc and she just may have hurt herself there, maybe even a scratch?
Exactly what i was going to say.
I was playing on our climbing frame when i was about 6-7 (i know it was before i was 8 cos we sold the house with the climbing frmae then) and i came down hard on one of the poles (not vertical!!) and there was some bleeding... Mum took me to the Dr's and it was put down to my hymen tearing.... still worring though.

Most active children tear their hymen well before reaching an age that it can be torn by sex.

Also could be thrush... scratching down there will cause a bleed as the skin is quite thin...

But second everyone else and say take her to a Dr JIC
xo