Your mother needs to translate her verbal guidance into formal, written instructions granting you power of attorney and specifying what compensation she wishes you to be paid for the various services you expect to be providing.
Setting aside the money issue for a moment, though, are you sure you're happy to take on the job? What's the background to your question, if you don't mind my asking?
https://www.agingcare.com/questions/mother-gave-me-access-to-checking-account-did-we-need-contract-431262.htm
https://www.agingcare.com/questions/mother-to-pay-2000-a-month-to-live-in-home-182257.htm
You can read more in this article:
Personal Care Agreements Can Compensate Family Caregivers
https://www.agingcare.com/articles/personal-care-agreements-compensate-family-caregivers-181562.htm
Setting aside the money issue for a moment, though, are you sure you're happy to take on the job? What's the background to your question, if you don't mind my asking?