Severe constipation

My 13 year old cat has been well maintained on a canned diet for her diabetes. BS levels have been in normal ranges without insulin.
   
Lately she has been experiencing constant constipation and had to take her for the first time last week to the vet for an enema.
   
She was put on Cisapride, has not done anything for this problem and had to be taken back this week for another enema.
   
An x-ray was performed, showed stool backed up in her colon, bloodwork, all in normal ranges, thyroid normal.
   
She was sent home with Hill's science diet w/D, canned, which she is not happy with and we also got a bag of Hill's I/D, which I have not fed her dry food in almost a year and am not very happy about but she eats it with no problem.
   
She is now on a half teaspon of mineral oil twice a day and the cisapride, 1 ML twice a day , the mineral oil was started this morning.
   
It is like she has no lubrication, her stools , the little she passes are hard.
   
I am desperate, pumpkin puree , organic squash, laxatone does not help either...