My ten year old shepherd mix at 6 years of age had pyometra had an emergency hysterectomy

My ten year old shepherd mix at 6 years of age had pyometra had an emergency hysterectomy. At ten years of age was diagnosed with diabetes is now insulin dependent. Had an ear infection and uti which was resolved with antibiotics. Has been aggressively knawing at both front and back paws been scouting for over a year and aggressively licking her genitalia, specifically focused on her vagina.Has had recent blood work taken and has an ionized calcium level of 1.6 the current vet recommendations are cancer or parathyroid disease. They prescribed zenrelia 8.5mg 2 tabs daily for what they believe to be a skin related issue. My concern is if it is bacterial my research has told me it could make the condition worse and with her compromised immune system, put her at high risk for other types of infection and over the long term have a more negative impact. I’m wondering given all the info provided if there could be other conditions elevating her ionized calcium and also causing her skin issues.