Registered Nurse

Left dorsal foot wound. Started as small non raised red areas and petechia. Progressed to bruised area minus open area when she went to ER. Three doctors saw it and could not identify cause or toe of wound. Wound open up in center since being in ER. She is current home care patient with other non healing wounds on right leg. (They don't look anything like this). Right leg recently positive for pseudomonas and staph. Receiving antibiotic treatment for that during dialysis. Minimal drainage. Current treatment is #Mupirocin cream and dry gauze. Any ideas on what caused this?