Hello and welcome to HCM.
Thank you for your query.
The cause for the blisters could be many, ranging from bed sores, uncomfortable clothing, poor hygiene, etc. If these recur a consultation with a dermatologist
and sending a sample of the fluid accumulated inside the blisters can greatly help in making a diagnosis.
You should also note that your patient is a diabetic and thus, healing will be poor. Please encourage good hygiene and avoid keeping the patient in bed for long durations without changing the patients position. Also provide comfortable clothing and sterile dressing when these blisters appear.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications. I would gladly help you.