How does one determine what to pay your relative for elder care as a caregiver?

If your mom qualifies for Medicaid, then she is low income. If she is applying for Medicaid to assist in paying an assisted living facility, then the majority of her money will go toward her care. If she is staying with your sister, then that's a bit tricky. I'd say pay what the utilities increase by, any extra should be decided between them. There's no fast and easy rule.

I just noticed your mother is in assisted living. Are you planning to change that circumstance? If your mother is in AL, she most likely wouldn't qualify under Medicaid for a caregiver. I don't know about this. Maybe others will know much more than I do about it.

One thing you can do is check the average hourly rate for caregivers and CNAs in your area. Around here it is about $12, but that will vary area to area.