Meet The Inconveniences
Now, as you know, I think that most of the reason that Elly feared her mother is that she had the nasty habit of giving a spoiled brat her right name and would have made a point of telling her that she would have pitched a fit if they'd tried to make her wear a uniform when she was a kid and only wants to do so now because she's a power-crazed loon. It's like how John's dad is an inconvenience because he remembers that the pompous ass he raised was a lot like the children who confound him.
Carrie Patterson is a lot like that but brings with her a worse peril she's a competent parent who can use that ability to get Mike, Liz and April to behave like civilized people while Elly cannot. Elly is always worried that she'll be replaced. John's mother makes that the best idea ever.