Mom has a lot of medical bills. Her only income is social security, Part A and B. Is she eligible for Medicaid?

Issues rearing their ugly heads: bankruptcy, creditors' liens on her home, complex Medicaid rules on preventing home from being included in assets that need to be spent down, probably more. You and your mom really, really, really need to see an elder law attorney who has Medicare expertise in the state in which your mother lives. A quick and dirty google indicates that there is a retroactive Medicaid payment program available by state but it doesn't seem to apply to your situation. DON'T LISTEN TO ME ABOUT THIS. TALK TO AN ATTORNEY.

Your Mom does not have a supplimental? I have a supplimental but have deductables and a "share" feature so we are usually paying out if pocket because we see a doctor about 1x a year. The "share" feature is applied to the 20% Medicare does not pay. We pay half of the 20%.

I too suggest that you talk to someone at Office of Aging. Mom can own a home, its her income that will be looked at concerning Medicaid for health insurance. In my State it covers medical, vision, dental and prescriptions. If Mom does not qualify for Medicaid, O of Aging can help her find a low cost medical plan or prescription plan. My Mom was on a State prescription plan. Dads employer provided her supplimental.

Does mom have part B Medicare?

It depends on the State, she may qualify for QMB Medicaid if her income is low enough, which would cover the co pays deductibles and co insurance that Medicare doesn't cover. Take mom to social services, they can determine if there are any benefits she can take advantage of.

What part of her hospital bill was not covered by Medicare? Is it her deductible, or co-pay?

Medicaid can be complicated and varies state to state. Have you googled "Community Medicaid i x state?"

Call the local Area Agency on Aging and ask for assistance.