We need someone to come in 1/2 days a week to help mom. She has social security and Medicare. What do we do?

If mom is already living in low-income housing, she will qualify for Medicaid. I'm somewhat surprised she is not already on it and in some sort of QMB between medicare & medicaid regarding her RX 's. The housing she is in, is there a cental office that coordinates transportation, a meals program, health screenings? If so, I'd suggest you contact someone in that office that to find the medicaid caseworker for her area.

Regarding have someone coming in to help, mom will have to be evaluated for the type of medical assistance needed. Just needing help with day to day activities like shopping, cleaning isn't medicaid. But medication management, PT, OT, wound care is.
Before you get into all this, it would be a good idea to schedule an appt with moms internist & you to go with mom to the appointment to find out what moms health status is like. To get into a NH, she will need to clearly show to be "at need" for skilled nursing care with documentation in her health chart as to that need. Often for those living at home or still independently, their health history just shows a relatively heathy but aging elder. You need to speak with her MD to see where she is for need. Mom may need to switch to a gerontologist to get her health chart to be more detailed.

Also states are moving away from 1 on 1 programs of assistance to group services at a center like PACE as they are more cost efficient. If your state is doing PACE, mom will first go to that for 2 - 4 days a week for meals, medical care, other social services with transportation provided and if the PACE center cannot meet her needs then she gets 1to1 services up to a certain # of hours per week based on a medical evaluation. Maybe 28 -32 hrs a week maximum. More than that tends to be viewed as not cost effective and they need to be in a facility

Pat, see if your Mom could apply and be accepted by Medicaid.   Depending on what State she lives in, that State could offer programs that might help.   Call her State Medicaid office, or try to locate it on the Internet.   You can also call her county Agency on Aging, they are a storehouse of information.

Depending on your Mom's Dementia, she might be able to move to a nursing home and Medicaid would pay for all her care.