She needs to keep taking what the doctor prescribed until they say to take her off it. Most likely it's the med that has caused the numbers to stabilize it, so taking her off could throw her back to where she was before. After a period, you can discuss with the doc to remove the med if you would like and see how she tolerates it. Then retest to see how high the levels are and monitor.
Also low vit D levels can contribute to high cholesterol levels. It's controversial at this point, but I know someone who had extremely high cholesterol levels at pregnancy and the doc said it was because her vit D was low. She was given vit D and then the cholesterol went down. Could be different factors, but it won't hurt to check vit D levels.
Fenofibrate is mainly used to reduce cholesterol levels in people at risk of cardiovascular disease.
If your mother stops taking the medication, her cholesterol levels will probably rise again which in turn increases the risk of cardiovascular disease.
There is a lot discussion going on about the effectiveness of cholesterol lowering medication but large tests have shown the benefit of it and most cardiologists have the same opinion.
Normally, the medication is taken the whole life of the patient, but you of course can discuss medication dose or medication stopping with your doctor. He/she knows what risks it will mean in your mothers situation.
If it is because of side effects that your mother would like to stop or lower dose, keep in mind that there are many different cholesterol lowering medications, each with different side effects.
Also here, discuss with her doctor.
Good luck!