So a while ago I went to see a production of Mamma Mia, and since I can't deactivate the part of my brain that wants to make everything about my favorite gays, when Sam Carmichael said something along the lines of "I'm just a divorcee that has been in love with you for 21 years" my brain went automatically "omg, omg, omg, sachston, omg".
At the time, I kind of pushed the thought away because I wanted to pay attention to the play. But I'm thinking about it now so...
Imagine like, Sachston in a Mamma Mia situation, not the three possible dads thing, but like, maybe an alternate universe where the events of dwp2 never took place, so Emily and Andy never reconnected. One of Emily's children is already 20 or whatever and is going to get married, and the other is going abroad to study very soon. They are both kind of worried about their mother because after a long streak of bad relationship with men (that never ends well because Emily is a lesbian in deep denial, and also very bad at choosing men), she has been single for a while and she is also lonely in the friendship aspect. So the children are afraid they are going to be leaving her alone.
One day (a few months or even just weeks before the wedding), they find an old box with the stuff from Paris, and some stuff about Andy Emily collected without meaning to (or at least that's what she tells herself) along the years, old articles, newspapers, etc. They start to dig in and discover that Andy is just some old coworker of Emily, but that she's also clearly important enough that their mother kept all these stuff with her throughout decades.
After a lot of Google searches and background checks to make sure Andy is a good person they decide: let's invite Andy to the Wedding without telling anyone to see if we can help our mother reconnect with this important person from her past (initialy not necessarily in a romantic way).
Andy is obviously thrilled when she gets the invitation, thinking it was Emily who was inviting her. She appears in the place the wedding is taking place (that could be a greek island if you wanna keep the Mamma Mia vibes), and is welcomed by Emily's children, she is like "omg is so great to meet you, where is your mother I wanna say hi!" And they're like "yeah, that's not going to happen, she doesn't know you're here". Andy is like ??? And they lie about how Emily is always talking about the "good old Runaway days" (which she obviously never does) and old friends, so they decided to invite Andy as a surprise for her. Andy, of course, panics because if Emily didn't invite her, then she shouldn't be there, and she should go before Emily finds out, because how crazy would it be if Andy had just dropped everything she had to do to go to the wedding of some random kid she doesn't know just because she thought a person she hadn't spoken in more than 20 years invited her? Haha. But the kids convince her to stay at least for a while.
When Emily finds out that Andy is there, she is livid because, omg, what the hell is she doing there??? And right before her kid's wedding? Emily can't deal with it right now. Yeah, she is happy to see her again, but she is also angry, because she has also old unresolved and complicated feelings about Paris, and Andy leaving without a note, and that phone call Andy never answered, and whatever.
Not wanting to get the children into trouble, Andy lies saying it's all a complete coincidence. And Emily is like "alright then, stay, but i don't wanna see you, I'm too occupied with the wedding". And Andy tries to stay away. But stuff starts to happen, like problems with the wedding, with the flowers, with the food, with whatever, and Emily is going insane trying to deal with everything alone (because the children's father, Emily's ex-husband, ofc, is useless, and is not even there yet), so Andy's problem solving skills kick in, and she starts to help Emily. They start to spend more time together. New and old repressed feelings start to grow. Andy starts to bond with Emily's children, too. Something, something, something. The wedding day runs smoothly thanks to Emily's and Andy's share efforts (unless you wanna add some drama to stir it up). And when it all ends, the only thing left for them to resolve are their feelings for each other.
Of course, everything ends well, and they live happily ever after.