One person may designate another person as having authority to handle legal matters on the one person's behalf.
The instrument which accomplishes this is called a power of attorney.
It may be a broad power, encompassing authority to do many things, in which case it is called a general power of attorney.
Or it may be more limited and specific, in which case it is called a special power of attorney.
An ordinary power of attorney however terminates automatically just at the moment when one needs it most, for example when a person becomes disabled or incompetent.
For this reason you need to request a durable power of attorney. It may avoid the trouble, cost, and expense of guardianship proceedings.