Oh bless her, she does look quite sorry for herself, poor little girl. With that level of urine staining it is likely she's been kept in a filthy cage until recently so hopefully she hasn't been outside too long. She is a dumbo roan, does she have nipples along her tummy? If so she's definitely a girly.
As she's been outside she will need treating for parasites with ivermectin (as in Beaphar Spot-on), and a course of doxycycline from the vets to protect her from leptospirosis (Weil's disease). Doxy treats respiratory problems too but might be a good idea to give her it combined with Baytril to really knock her respiness on the head. Bizarrely that scab is in a very common place for Baytril injection burns... could just be a coincidence though!
Do you plan on keeping her? If so please quarantine her for at least 3 weeks before considering introducing a friend, to make sure she's not caught anything nasty and to ensure she isn't pregnant.
Definitely recommend you post on Fancy Rats, it's very friendly honest! Big well done on taking her in and looking after her
