Homeopathy isn't "natural medicine". Homeopathy isn't medicine, period.
As for natural cholesterol medicine... first of all, there is zero reason to believe that anything "natural" is any less likely to cause side effects. Many "natural" cures only lack side-effects because they lack actual efficacy, working by placebo alone.
If there were effective "natural" remedies for cholesterol, chances are your mom's doctors would have tried them already. After all, "natural medicine that has been proven to work" is simply referred to as "medicine". Paclitaxel, a compound isolated from yew trees, has been shown to be highly effective for various forms of cancer. The healers who have used it to treat countless cancer patients are still called "oncologists", and the ritual for administering it is still called "chemotherapy".
IMO it might be better to look into adding on a different drug to fight the stomach issues, or to try and reduce the necessary dose through diet and lifestyle changes.