When a delusional young woman is confronted by the closure of her uncle’s vintage car dealership, she must travel cross-country to see it one last time.

I believe it would be more effective to specifically indicate the action taken by your protagonist. Why does she need to see it one last time? How would she change from seeing it or not seeing it? Does the fact the uncle specifically ran a vintage car dealership have something to do with her trip (possibly by car)?

The "delusional" description is quite intriguing, yet doesn't evidently fit with the event or action as far as this logline reveals. I feel there's more to the story, which could be incorporated into the logline.

Either way, it's a very nice logline!
Good luck with writing and revising!
– Joshua L.

I like the vintage 35mm/Little Miss Sunshine feel this gives me. I assume she wants to go to the shop to reminisce, but maybe whatever it is should be clearer in the logline. The narrative potential the "delusional" aspect has really excites me

It is unclear how the woman's delusion is connected to the story, or whether she can somehow overcome it.
Also, we could do with some higher stakes. Why should she see the dealership again?

Maybe put the event first and then the character?

I think the proper format should be:WHEN (An EVENT happens), a (CHARACTER) MUST (do the ACTION)