I read or watched an interview with creator/showrunner Liz Feldman and where she said that the ending wasn’t actually her idea but was brought to her by another writer on the series. I would link to it but I read a lot of interviews about the show and can’t recall which this particular point was mentioned in. So it sounds like her original concept was maybe a little more grounded and more about Jen and Judy’s relationship. I think a lot of shows, especially series made for streaming platforms, go the twisty-turning route because it draws people in and gets them talking. The more people talking about that crazy thing that happened in episode so and so on social media, the more attention the series gets. I don’t think two solid performances about grief is enough of a draw anymore, sadly. That said I do think the writing and the acting balanced out some of the more outlandish twists, with lesser talents things could have easily veered off into the ridiculous, and while the ending is a little far fetched, the emotions and pathos still feel very real.
ETA: Found the article if anyone's interested: https://ew.com/tv/2019/05/09/dead-to-me-creator-burning-questions/?fbclid=IwAR0Ie_Mcd5TBBeWwPLDCGeRH6MfE3aWOyTB9hgQw5rkrrKnQ11QfeVgCbQs