Mom w/dementia, lawyer says I need to come in. Does anyone know why I would need to go in?

We already did the deed (that sounds kind of punny). The house is to go to me once she passes and we filed the paperwork with the county already. The trust has been funded and everything done, there is an exempt trust and a living trust. I'm thinking they want me to try to get guardianship, which is expensive and time consuming, and I have no interest in doing that.

I feel your frustration. If you even ring and ask them to be more specific about the appointment, the ratbags will probably charge for that too.

But it's outrageous that the assistant couldn't answer your reasonable questions. Money aside, they're asking you to spend your time on this - obviously you need to know why it's necessary to attend the office and what documents they're talking about. Honestly!

I think I'd email The Big Himself and ask.

Who's the successor Trustee? (It's not the same thing as an executor.) That's what's important, because a POA is no good once she's gone.

If your mom has a properly set up will and trust, I'd really wonder what the attorney needs. You should be able to send in the doctor's letter for his files, but I'd question what he needs, too.

Sounds to me like the assistant is fishing for billable hours.

If you are already set up as acting POA, then there is honestly nothing else you need to carry forth this duty. If however, you have not taken this POA to a bank, and/or a bank has refused it because documentation has not been completed, then you do need to do this work with a lawyer, and yes, JoAnn is correct that your mother's funds pay to do this.
Some POA were written as part of the senior's documents. It will say RIGHT ON THE POA itself under what circumstances you may serve. Usually it says that the assessment of two doctors is required to enforce the document, that the senior can no long act in his or her own behalf. That is the norm on a POA done before there is a need. Then the Lawyer writes you a letter of certification that you are now POA for the Estate and he files the letters from the doctor.
So read your POA document. It will say what is required for you to act as POA right on the document itself. Also, tell the office Secretary that you cannot come in until the Lawyer tells you exactly WHY you are coming in and exactly what you need to bring with you. It should not be difficult for you at this point to get the documentation of the MDs for him if this is what is required.

Anything the lawyer does should come out of Moms money. I do agree, that it would be nice to know what he needs u to come in for.

You have every right to ask specifically what the attorney plans for this visit.  You can also ask what data you need to bring (so you'll be prepared).    If the attorney balks, either keep insisting on more detail or don't go.

Given that a trust has been executed, it might be that the attorney wants to handle "funding" of the trust, something which you can do other than transferring real property.   Only an attorney should prepare the deed; you could record it, but I'd let the attorney handle that as well.

You can also ask why you can just send the doctor's letter to the attorney.

My attorney drafted everything in one setting.  We had one meeting for discussion of issues and a second to review and execute the dox.   We also had signed a retainer letter with a specific cost for the dox prep.