Testing for cognitive function?

My mother is 89, and in Assisted Living. All her life she has been very nasty and controlling with everyone in the family. Now she is trying to claim that my sister and I are “trying to take her property”. All that has ever mattered to her in life is her money, and she is well off. It’s getting more difficult to keep her from getting in financial trouble as she will respond to every get rich scheme in magazines, etc. we have a POA, but it’s even difficult to get some places to respond with that. Neither of us can afford her care, but I know she has the funds to do it. Yesterday she announced in front of several others that she knows we are trying to “take her property”. I am the only one close to where she lives, and she relies on me to get personal items, but I’m about at the end of my rope. How can we get her tested so we can get some kind of control before she ruins her finances and has no where to go? She keeps falling and has broken several bones.