My mother has Alzheimer's and is having a terrible time with her money. How can I become power of attorney to oversee her affairs?

Too late. A power of attorney can only be granted while the principal is competent. If you have no such document in place your only option will be petitioning for guardianship. You might as well start researching this now because it is going to take months to get done. Sorry, but perhaps your mother's mistake will provoke others to action before they get stuck as you are.