RORY: Mia, why don’t you move back here? We miss you.
LORELAI: Or at least visit more? You used to check in. You never come at all.
MIA: I don’t have to. You’ve made me redundant.
LORELAI: I have not.
MIA: Don’t be humble. The inn is beyond covered. It’s never run this well or been this successful. That inn is like your place now. Without you I wouldn’t know what to do, I’d be lost.
An explanation for why we’ve never seen Mia before – she lives a long way away, and Lorelai is doing such a good job of running the Independence that Mia doesn’t need to check in with them any more. This unexpected visit from Mia seems to be almost purely nostalgic, and perhaps timed to coincide with the Autumn Festival.
Of course, it leaves Lorelai feeling very guilty. If the Independence can’t function without Lorelai, how can she and Sookie ever quit to start an inn of their own?
The Annotated Gilmore Girls 