Hi - Unfortunately, the side effects from Arimidex hit some women quite hard; and there's not much you can do to effectively treat them. If she experienced joint/bone pain, over-the-counter drugs (ibuprofen) might help; and exercise seems to relieve stiffness. But since she's stopped taking it, I'd guess she already tried the obvious remedies, and they didn't work.
Stopping Arimidex raises her risk of recurrence. By how much, her oncologist would have to tell her. But she might suggest to her onco going on tamoxifen, which seems to carry less painful side effects. It's not as effective as Arimidex, but it was the hormone therapy drug of choice for over 30 years, until being supplanted by the aromatase inhibitors about 10 years ago; and it's better than nothing. So, it's worth asking about. Take care- PJH