By supplement, do you mean Medigap and/or Medigap? Check your supplemental insurance policy. In some cases, Medicaid itself helps pay for long-term care - but of course, there are restrictions. Here are some guidelines:
Generally Medicaide WILL pay for nursing home care BUT you must first spend down your mom's assets to about $2000-2500 depending on the state where she lives. The easiest way to understand what's possible is to talk with the Business Office or medicaid specialist at the nursing home. It's their job to know all these details to ensure the company gets paid. Medicare will pay for up to 120 days of skilled nursing home care is the intent it to rehab someone to go home.
https://www.agingcare.com/133610