Will my mom get penalized for the years she was covered under my dad's insurance plan when joining Medicare Part D?

It's not likely that she'll get credit for the years under your Dad's plan, but you can check with Medicare. Unfortunately, she just missed open enrollment, which is the time people can join without penalty (or make changes). You could ask Medicare if there are any exceptions to this rule and tell them your mother's story. Maybe they can help. The only way to find out is to call and ask. Good luck,
Carol

Thanks Carol, that is exactly what I did. She will be penalized for the 16 years she did not join, amounting to an estimate of 20.00 a month more for her preminum. It will be difficult to prove the coverage under Dad's plan since the entire company was bought out and reorganized. The union may have some information that will help her. She is very cheap and resistant to get the coverage because it will cost he rextra money, etimate of 50 - 70 per month extra. She has plenty of money for this coverage but is being difficult. This is the tip of the iceberg with her. Thanks for your input.