What is the maximum amount of time permitted for full payment under a contract for deed?

Adult child wishes to place 87 year old mother into a nursing home and to apply for Medicaid in Illinois on her mother's behalf. Adult child is thinking that a contract for deed, with the mother paying the real estate taxes and child being the purchaser, would be an option for mother to qualify for Medicaid. Adult child needs low monthly payments, which means that payments for deed should be extended for as long as possible. With a 5-year term, payments are over $2,000 per month, which is too expensive. Are there any options? Any suggestions?