Depending on what pain meds she is on that can also cause weakness and instability... my MIL was on the duragesic patch for a time and though it worked tremendously for a while, eventually she started getting more and more unstable and had several falls. Took her off of it and within a few days she was much more stable. Does she use a walker for support? That can also help to provide support when they are less stable.

Heidi