Do you need a Medicare Supplement after being accepted for Medicaid?

Since Medicaid is state run, I'd check with your mom's social worker. There's a "spend down" on Medicaid (generally). How that is handled is not the same in all states. Likely, the Medicare supplement isn't the best choice financially, but I'd keep it until you talk to the Medicaid people in your state. Sometimes, Medicaid would rather your kept the supplement. They'll help you decide what is best.
Good luck,
Carol