Using an Addendum to update Estate Planning docs

Is it possible to renew a set of estate planning documents by having the principal named in the documents sign a simple statement indicating that is his/her intent? The reason I ask is to come up with a simple solution to the following problem.

My elderly, widowed, Mother suffers from the beginning stages of dementia. In 2006, when the four older family members learned of her impairment, we hired an attorney to update her will, power of attorney, durable power of attorney for health care, and directive to physicians.

Unfortunately, we have a fifth family member who is a bit of a rogue and who knows how to manipulate our Mother. In recent months without discussing matters with anyone else in the family she took our Mother to an estate planning attorney to completely redo her will, etc.

I intercepted the attempt because I manage all my Mothers bill-paying. Because of her diminished mental capacity, she had no recollection of the visit. I had her sign a letter canceling the request. Phone messages to our rogue sibling have gone unreturned.

This has happened twice in the past few months. I've been fortunate to intercept the written communications so far, but there is always the possibility our rogue sibling will at some point instruct an attorney to send all communications to her rather than our Mother. At that point, we will not know the estate documents have changed.

My Mother has a modest estate ($300,000), and lives on Social Security and a small pension. Her estate documents are simple and straightforward. We are looking for an inexpensive solution.

One thought is to take our Mother to the attorney who last updated her will in 2006, and have her resign everything. And, repeat that process every few months. But that would likely be expensive.

Another thought would be to request blank versions of the estate documents prepared in 2006, and have her sign those every few months. That seems cumbersome (initial every page).

Our thoughts were to draft a simple, one page document that references the existing 2006 documents, and states they are current and all others are revoked.

What are your thoughts? Is a single page addendum a viable solution?

We have investigated the possibility of pursuing Guardianship for our Mother. But that would be costly and risky--although she has diminished mental faculties she may not be deemed incompetent.

Any other ideas you think helpful would be appreciated.