It's best when we keep things simple, but the friend might ask for an initial consultation with a local attorney (most often in cases like this the initial is free). I foresee inevitably this would involve probate. I went through this with both parents.

If they are named as Guardian/Conservator (in some states, they are separate) yet a Durable POA in my experience for the friend would work. If a physician has 'officially declared' a dementia diagnosis - it could be dicey having the taxpayer sign anything.

It's a great person that is stepping in - it can get rough. The more they 'know' ahead of time, the better off the journey will be.