Imiquimod - How long do side effects last after ending Aldara?

They are many differences between patients. Those that have stronger reactions, particularly sores and even bleeding, have a better long term reaction. I have pretty intense AK, about 200 individual leasions. These were on my face, shoulders, arms and chest. My chest was the worst, painful, and it took a long time to recover. I had 100 leasions. It took 6 months for my skin to look normal. After several years I treated my chest again, but had 12 leasions. They still were very painful, red, sore. But my goal is to prevent further disease. I am 71 years old.

For myself, the noted side effects - including the flu-like symptoms - were definitely present but seemed to noticeably relax after 2-3 weeks. However my Dermatologist had discussed the side effects with me before starting treatment for AK, and he told me to see him if the side effects became too onerous. They didn't, and I felt no need to see him regarding them.
The Aldara treatments did work very well in the long run, but one has to stick to it through the difficult early going.
However, I am 68, whereas your mother is 86 ... a big difference and the age may make a difference in her responses to Aldara. I definitely think you should see your doctor about her side effects just because of the age factor.
Hope this helps.