Mom had $80k and loaned us $65k, then she forgot. We have a signed contract and we make regular payments. Now,18 months later, she's saying we stole the money. What can we do about this?

This might be out of the question-especially in today's financial market, but you may consider tryi g to get a loan to repay her the balance of what you owe her- even f it means mortgaging your home or other property. My advice would be to pay it back as quickly as you can!

Problem is that she sees the contract, and sees all the checks, but is now telling everyone (family, neighbors, strangers, church, lawyer) that we took the money without her permission, then made her sign a document - not true. Payments are made on time or early and non of these accusations have come up over a year and a half of payments. I'm worried that the situation will be our word against hers as far as the document. (She has also eaten salmon from cans found in a dumpster because her dog said it was ok which tells you her mental status at times. Former primary care doc (good guy)thought she has multiple personality disorder - never told her -she won't see that doc again because 'he looked at her like she was crazy').

I'm not sure what the exact question is. You should be able to show her the signed contract and deposit/payment history if it is your mom who has questions about where the money went and how it is being paid back. Is there a threat here that you took the money without permission and will be reported to some authority or another sibling involved? Sometimes as our family ages, they can "forget" activities that occurred over time or if they are challenged about it. Show her the signed documents and payment history to reassure her.
Helen