Is Medicare Part B Required to Stay on Supplemental?

My Mom is 85 yrs. old and has enjoyed full medical, dental, and vision benefits as a Prime Care Survival retiree with Edison International since she was 65. Under her coverage she has no deductibles or premiums of any kind. This is one of the best health coverages on the planet.

My Mom received letter from EIX Benefits that she must enroll in Medicare Part B to remain in an Edison sponsored health plan by Mar 31st,2015.

Upon further discussion with EIX reps. they said they were complying with Federal law, which one I ask them? And there still trying to figure that out.

My question is, does this situation have anything to do with the Affordable Care Act or Medicare ? I thought I heard President Obama say, ” if we liked our present health coverage we could KEEP it. Why would my Mom trade her no payment plan for Medicare Part B plan with all its payments, premiums, and penalties?