I incurred $4,000 of expenses taking care of my mother's property while she was in a nursing home. I would like to claim them as an itimized deduction.

No, you can not deduct those expenses. Under miscelleneous deductions you can only take:

1. Unreimbursed business expenses
2. Tax preparation fees, and
3. Other expenses related to yor income, including expenses:
a. To produce or collect income that must be included in your gross income,
b. To manage, conserve, or maintain property held for producing such income, or
c. To determine, contest, pay, or claim a refund of any tax.

It may have been appropriate since you had PoA to pay these expenses out of your mother's funds, and then (perhaps) she could claim these as deductions if they conform to the above purposes.