What do you mean by almost had a heart attack? Chest pain should be examined by a doctor. I would look into resources, such as free state insurance or whatever for low-income and poor individuals, and get her to a hospital. There is absolutely nothing you can do to stop it because you cannot prescribe her the medication she needs if she is having heart issues.
If you state your location, country or state, I can try to point out how to fill out applications to get the insurance she needs for free or low-cost. You can also go to a hospital yourself and ask for help on how to start the process of insuring her and getting her an appointment to get checked out. They will help you if you explain the situation and that you are worried about your moms chest pains but you can't pay for it.