The only way scale rot will kill her is if you don't treat it and let it eat her.
Do see a vet, better safe than sorry. Switch her onto papertowels for the duration of treatment, you must keep things cleaner-than-hospital clean. Get yourself some Betadine, and mix it with water to wipe her with or let her shallow soak, whichever she tolerates better.
The vet will give you antibiotics to treat her with after her Betadine. If you keep her clean and warm and treated with antibiotics, she should heal up fairly quickly.
Gale