Sounds similar my diabetic, 98yr old nan who refused to move from her home, and expected my 70yr old, disabled mother, to visit daily and do everything! Its difficult, and people like their independence. Sounds like she could benefit from several services (I'm no expert BTW, and people might correct me):
Social services: assist with what care options are available, prevent social isolation by checking what clubs/social things there are locally, if driving is an issue now, are there any local transport services available, elderly care groups, get-togethers etc. Also check what benefits she currently has and what else she might be entitled to and generally put her in touch with various services.
Occupational therapist: looks at the function and helping her remain independent. Look at her walking and whether a stick, frame etc might be of benefit. Looks at things in the home and risks, such a rugs she might trip over, would a handle near the step make it easier to walk in, would a long handled shoe horn help etc.
Nutritionist/Dietician: not only to advise on diabetic friendly meals, but also advise on losing weight. Also might advise a high protein diet to help the leg ulcers heal.
District/community nurse: wound dressings, diabetic checks (among other things)
Does she currently visit a diabetic foot clinic for chiropody care? Our area has cut this service except for the most severe, but being a diabetic, she could be entitled to this service too.
Also seeing an optometrist, again, due to the diabetes.
If driving is a safety concern/visual concerns I'd be speaking to her GP if she isnt safe and a danger to others.