One of my favourite clients is diabetic.
She loves her Gelish and the way her nails have improved since getting treatments.
After consultation I was fully aware of her condition, and I am super careful during her prep.
Doing a proper prep and Gelish treatment there really should be no need for concern as how could you cause injury or bleeding?
I asked on my training if there is anyone who cant have Gelish and was told nope. Its suitable for all, EXCEPT Do not use it on ladies over 6 months pregnant in case they go into labour. Hospital arnt aware how to remove it and it can cause problems if a c-section is needed due to not being able to see nail colour.
I have a few clients with diabetes who wear gelish without any problems at all although I would be cautious about applying it on toes.
I did refer one client back to her doctor to get the all clear and they advised against it. This particular client was in her seventies, had very poor circulation and very thin toenails although her fingernails are incredibly thick and strong.
I think if you are in any doubt at all i would advise your client to get permission from her doc/medical professional just to ensure you are protected yourself.