Peggy Sue Fic is probably the best idea. It is what they are called (for better or worst).
I'm not sure about the "fic" part - it seems to reinforce the current weird emphasis on this being a trope limited to fanfiction.
How about Peggy Sue Time Loop? It always involves a Time Loop as a central element, after all.
Fiat iustitia, et pereat mundus.That still doesn't help with the opaqueness of "Peggy Sue". Just who was she again? Should I know her? Where is she from? She sounds like some Sourthern USA farm chick.
Peggy Sue Plot is probably the best if we don't want to limit it to fanfic (although there is no genre that has embraced this trope more than fanfic, the movie might be the trope namer, but it's in fanfic that it is ubiquitous).
Then how about renaming to Peggy Sue Fic, for the sake of clarity?