A: A beneficiary can become the Trustee if the Trust allows for such an occurrence. One would want to have a new Beneficiary of the Trust and/or a new Trustee appointed as soon as possible because you don't want the Trust to have the same Trustee and Beneficiary if it can be avoided.
A: Short answer: Yes, it will hurt your credit. If your name is on the mortgage and it is being reported to the credit agencies, then as soon as that mortgage is reported as late that will be a ding on your credit. You can dispute your responsibility for the expenses with the agencies, but until your name is off the mortgage via a refi or payoff, then your credit will be impacted if she does not make the payments.
A: Usually, you would have the deed carry forward the description as you received it and then add at the bottom a line something like, "Address of the property being 3 Oakdale Lane, Lincoln, Massachusetts." You would also indicate the property address on the left margin of the deed. There is no need to do a confirmatory deed. I'd be happy to help with your downsizing sale. I have clients in Lincoln and am familiar with the area.