SI joint dysfunction; herniated discs; sciatica;

or some type of arthritis. There could be so many reasons for low-back pain, especially given her age. She probably should get an X-ray, MRIs(for the lumbar and maybe sacrum/pelvic area), and see a rheumatologist for further testing (blood test, etc.).

I have SI joint dysfunction, and some of my symptoms are similar to your mom's. But even for people with SI joint dysfunction, they can have different symptoms.

Disclaimer: I'm not a doctor ("not the kind that help people").