How do I get my sister to show us mom's financial records after she ignores a demand letter from our attorney in NJ?

As POA she can probably, if permitted by the document retain an attorney for herself. If she is using Mom's money for her own uses, that is called financial exploitation. You could call Mom's credit card company, tell them that there are charges appearing on the card that she has not made. You could do the same with any of her accounts. That is what Adult Protective Services would do, but you could get it done quicker. Tell Mom's bank the situation. They may perform their own investigation, though without POA they will not give you information. This happened in my case, APS made a call to the bank and all of Mom's accounts were frozen following their own investigation. If they suspect what you tell them is the truth they are required by law in most states to notify the authorities. And those reports would be taken more seriously than if a family member does it. Effective way to elimimate the family dysfunction.

Thanks for the replies
We have bank statements and credit card statements and recently went to the prosecutor.
We want to wrestle financial control from her as fast as possible
Expenses included a day at a water park ($300) meals, groupons, gas charges etc
I think we can prove credit card fraud (her name is not on card), ID theft (she recently opened a new card using mom's SS#, supposedly to get a better interest rate on one of mom's cards that had a balance on it but also charged $600 on it for car repairs)

I guess what I'm saying here is, a shopping trip to Kohl's could be for clothes for mom. I once bought mom 6 pairs of shoes so I could try them on her at the NH, returned 5 but the credit didn't show up until the next month. Does (did) your sister have a caregiving contract with mom? Make sure you know what is going on before you make an accusation like this.

What proof do you have? What is she spending mom's money on? Pam is correct, go to the DA in the jurisdiction where you mom lives with the evidence.

If you have proof, you march into the DA's office and present the proof. Won't cost you a dime.