What age? Have you any other chickens, has she been pecked around the vent?
Is it her vent that is bleeding or has she just got blood in her faeces?
There are two options, she has coccidiosis which is a parasite which destoys the gut lining and it bleeds and that is passed alomng with her faeces, or she has been pecked around the vent by other birds and they are continuing to bother her.
The spelling is Wyandotte and welcome EstherJ. If you can describe more fullyor take a picture would be even better.
HOw long has she been like this, is she laying or a young bird?
Labrador lover for yonks, breeder of pedigree Murray Grey cattle for almost as long, and passionate poultry person for more years than I care to count.