I think this sounds more like a pyometra as well. She doesn't have fluffy bedding does she or anything that could cause a blockage?
Drinking a lot is another symptom of pyo and the swelling is worrying. Antibiotics will give a period of respite but if it is a pyo it will come back.
There is some good info here:
https://vectishams.webs.com/pyometrainhamsters.htm