Asked on 02 Jan 2019
This is difficult to deal with. Because you are a "junior", persuading your mum to stop is not going to help as
1) She's likely hoping for a cure
2) She's emotionally invested hoping they work
3) She at least felt that she's being "helpful" by seeking alternative treatment
The best way is to get people of the same age or at least those she listen to, to talk to her. With you advising is a start, but you will need people to help pursuade her for a greater chance of success.
While your mum probably has the best intentions, it might be worthwhile for her to think about how your sister is feeling, being ploughed with all the talismans/miracle cures while enduring her current illness. It's not easy to feel sick, and being presented with countless options on what could potentially cure her. It would be even worse if some random healers were brought in.
I would not encourage spending any money on such things, not because it is a waste of money, but it could potentially be dangerous.
Once your mum recognizes that, she would probably turn around.
The focus should be on practical ways to treat your sister, and seeing how best to ensure she gets the care she needs. Health is the most important, at the end of the day.
If your family situation allows for it, let your mom spend on it (If unable to, try putting a cap). While those may not have verified benefit to the illness, it can give your mom an opportunity to try. Quite likely to have regrets and all if she just watches and not do anything. As Tat Tian mentioned, you can arrange to have her interact with people who are/were in similar predicament or other elderly folks (peer pressure).
Sometimes you need to "cure" the heart of the loved ones... When my dad was diagnosed with cancer many years back, a new neighbour enthusiastically intro a miracle drink read mlm. I know what's that all about yet I still allow my mum to listen to her and take the sample to "try"...
I heard of friends in similar predicament and when all else fails, bringing the mum to church to understand what is the true cure work (all the time).
It may sound unreal, but try it.
And for all you know your sister's illness can also be cured from non-medicational way.