Well, you mention that mom is a "senior citizen." Is she on Medicaid? If so, they should cover at least 80% of the cost. Also, has she not worked in a long time - if so, she may qualify for disability. Depending on what type of surgery she needs for her feet (like if she is diabetic) there are many, many places that will attend to her needs the very best they can.
Investigate more in your state/largest city you live near. I'm so sorry that your mom is sick. I have bad ankles and will eventually need surgery, so, I can kinda understand her pain.
Good Luck & Take Care!!