S.B.
I have a lot of experience with this as a Health Insurance Agent.
My advice is to NOT drop her Plan F. Please!
Plan F picks up where Medicare leaves off and it's the plan I signed my own mother up for when she turned 65.
By law, Plan F is Plan F. The benefits are all the same. The only difference is the premiums by carrier. Trust me, if you do some research, you may find a carrier that costs less and I have changed people from carrier to carrier every year during open enrollment. The benefits stay exactly the same. By law.
AARP may not be the cheapest for your mom.
I think you should visit a local broker in your area. Quotes are free. They can give you rate sheets for the different carriers. Then, you can decide on changing which COMPANY to go with, but by all means, PLEASE don't change your mom's Plan F. If you downgrade and God forbid something happens, you can't go back up.
Compare the rates. NOT the plan. Not at your mom's age.
My mom has Plan F and she has had gall bladder surgery, arterial stints, eye surgery, pre-cancerous lesions removed from her hands....
She has paid NOTHING except for her premiums for medicare and her Plan F supplement.
I know $190 seems like a lot of money. You may be able to get the same coverage cheaper. But, even if you can't, you know that your mom will be covered for unforeseen events. I, personally, wouldn't risk losing that coverage.
I would also like to say that I am not affiliated with any brokerage or agency at this time, so I won't recommend any carriers or angencies. However, I urge you to find a knowledgeable broker close to you to run the numbers for you.
I give people the same advice I'd give my own mother.
Don't change plans right now.
Best wishes.