Whew!! glad I spotted this post before your 10:00 appointment.
If a client is diabetic, it does not contraindicate a manicure.
You must be very gentle and careful not to abrade or cut the skin around the nailplate ... diabetics have very poor circulation in their hands and feet and healing is a slow process and wounds can becme badly infected very easily.
As an illness, diabetes is very well managed these days and normally diabetics lead very normal lives (my mother had this condition so I know it well). Just take care and let your client know you are taking care.
As nail technicians we should treat all clients as if they were diabetic and maybe there would be less willfull damage done to nails.