What can I do if I think POA is spending much of her savings for their own personal benefit?

The Durable POA is the person in charged of assets.And will be the person to explain all spending when it's time to apply for Medicaid.If the elderly is on Private pay.There really isn't nothing you can do other then getting the current POA revoked.Means you need to talk to a attorney that did the POA. With-out proof you have not a leg to stand on.When the elderly runs out of assets and forced to apply for Medicaid.That's when the POA will be questioned as where did the money go.If the elderly was not stated incompetent.The elderly has the right to do what he or she fits with their money.If the POA is spending wrong the first sign is double buying.Buying two of each item for the elderly and same item for the POA.Also,look out for checks being wrote out in children/Family names.The first thing to do is ask your self how would you hide money if it was you.Look in Freezer,Cash wont burn-up during a house fire if cash is in a freezer.I had a Uncle yrs ago placed $20,000 cash in a zip lock back of chilli in a freezer.Elderly people know how to hide money.......

You get proof of your suspicions, then take action.

It depends on your jurisdiction, but in some states, a document appointing a Power Of Attorney has to file the document with the Register of Deeds or courthouse and ALSO file annual Accounts which lists the expenses, with receipts to show where the money went. It's reviewed by the clerks to ensure the POA is acting appropriately. NOTE in some documents, the person who gives the POA says that the POA does not have to file an Account with the court. I'd check that first and then an attorney.

You petition for Guardianship. Cite financial mismanagement in the petition.