Does anyone know where to find a “Shared Living Expense” form? I looked on Legal Zoom, but no forms are tailored to my situation

90-yr-old mom lives with hubby and I. She fell ill last year and we had to move to one level home, and I had to quit my job, so that she could move in and be taken care of. She is on 24/7 oxygen and a walker. She pays 1/3 of the expenses and 1/3 of rent. Eventually she will have to go on Medicaid and to a nursing home type situation. I need a legal doc showing she is paying us because of the 5 yr Medicaid look back. I do not have the $$ to pay for a CPA and was hoping to find a doc we could get notarized that would work. Any suggestions would be appreciated. Thanks in advance!