By irrelevant, I mean the k-1 amount, not the entity. This is a pretty classic ASG. I'm betting that they are paying Betty a w-2 from Company X, because the k-1 to S Corp A is 25% of the total and the k-1 to S Corp B is 75% of the total. That's their way of evening things up. Company X should be the sponsor with S Corp A & B as participating employers. Everyone would be getting w-2 comp from one of the entities, so it's a pretty easy allocation.
Did she have a named beneficiary or beneficiaries? If not, what does the plan language have for a hierarchy of beneficiaries if no one is named? IMHO, you have to follow through that process.