How can Medicaid pay for mother to care for disabled adult child?

We have a potential client who is currently being paid by another agency to take care of her disabled adult child. The mother wishes to move care to our agency, however, I wish to be fully compliant. Where can I find chapter and verse in the Medicaid legislation to document this is compliant? If I recall there was something about guardian but under no circumstances could a POA be paid but I somehow cannot put my hands on this specific verbiage.

Thank you very much for sharing your expertise and guidance.