Lazy Bowel??

Hi everyone. Have been some searching on the internet, but thought I would pose a question here. My MIL(92) has had constipation problems for years and years. Her daughters keep getting her to take stuff to soften stools, etc. The last few years, she has started to have abdominal/back pain, enough to the point that she is sometimes quite ill. I am thinking that her bowel is now very lazy after taking so many laxatives, etc, and she doesn't empty on a regular basis. We had her take fibre for awhile, but I don't think she is anymore. She takes a stool softener, and eats a bit of bran for breakfast. I don't live close to her so can't say for sure what all she eats. I know she needs to drink more, and eat more fibre, but it's hard to convince her of that. She usually goes to exercise in the mornings. She has been to a naturopath/homeopath who does some stomach manipulation for her about once a month, and that has helped immensely. Heat also helps some. But her attacks now seem to come more often. Has anyone ever dealt with this, and does anyone have any suggestions or ideas that could be tried??
She has had many tests over the last several years and no one has come up with anything.
Thanks so much.

Glenda