I think probably your mother is having beta cell
burnout of pancreas
,which is a normal occurrence in long standing diabetics.When such a situation arises,no matter whatever dose of sulfonylurea
ureas you give,it is not going to increase the insulin
production from the pancreas.
I think she is in need of injectable insulin since her blood sugar levels are very high.
However you may consult a diabetologist
and get your mother thoroughly evaluated.
He might try some newer anti diabeticsehich may help your mother but in the end,injection insulin would be the right choice for your mother.
Discuss with your doctor about it and kindly don't increase the dose or change any medicine of your own.