@1spooky2me's Fixer-Upper AU Bill is so Blorbo to me. I wanna pat him on the back and tell him he's doing his best and that's what matters. But alas, that is what OCs are for.
I imagine Ford wanted some time to think and just kinda shipped Bill off to Nell's home on the other side of Gravity Falls for a few hours after some sort of altercation between the two of them lol. Nell being a witch who turns all of GFs weird paranormal energy into magic she can use ends up being a neat thing for him to learn about another person, at least.
More rambly character stuff under the readmore (These are mostly for me cause I love elaborating on concepts lmao)
In Nell's canon, she begins to befriend Stanford right around the time of the portal incident with Fiddleford, but ends up chased away when Bill has possessed a sleeping Ford and tries to kill her when she checks up on him (When Ford takes back over, he refuses any help she might offer and chases her off). She then avoids the Shack like the plague for the next 30 years, only to be roped back in the summer that Dipper and Mabel arrive in Gravity Falls
Nell isn't really one to hold grudges, but she is a little fascinated at Bill's arrival as a human on earth. She wonders if this "redeemed" man even remembers what he did to her.
Since Wierdmageddon, Ford has been able to actually pursue the friendship with her that never got a chance to bloom back in the early 80s, and that's why he was comfortable leaving Bill with Nell. Worst she's going to do is make Bill garden with her anyway lol