I may need to change my Mom's supplemental insurance.

You should have her on a part c supplement plan to cover the 20% not covered by medicare. One hospitilization or procedure could cover the whole years premiums. Also part D covers is very in expensive and many people do not realize if you do not sign up for a part d plan at age 65 when you do sign up you face a monthly penalty for the rest of your life. I wrote an article on this penalty and would be happy to share with anyone who requests it. Just pm me and I'll share the link.

anareus, personally, I would not want less than a C plan. No coinsurance coverage for skilled nursing could cost you $100 a day easily. Go to your state's website, enter your zipcode and get quotes from the top rated carriers.

She has A of the medigap plan. It does not appear to cover skilled nursing facility care coinsurance (not sure what that means), or the part B deductible or part B excess charges. Do I need to be concerned?

Are you referring to Medicare Parts A & B, or some other, perhaps private, plan? If she's not choosing a private plan or has a private plan from a prior employer, Parts A and B are the minimum she should have. A Medigap plan will pay the 20% not covered by Medicare after it approves amounts for various services.

As to the other Medicare plans, we haven't had any need for them, especially for D, as the premium cost is more than the cost of medicines my father needs.

What you need to do is list what expenses your mother has had, the out-of-pocket costs she has and compare those to what would have been paid under the other supplemental plans. Then compare your costs to what would be the cost of premiums under supplemental plans and what you could expect would be covered to find out if you'll be gaining or losing financially.

There are also other private plans, but do your research before selecting any of these as they can be picky in choosing what to pay under some circumstances.