A few notes/critique points:
Agnes was a short woman, and might be described as energetic or enthusiastic, but only if she was talking; any other time, she was a dried husk of a woman. Fortunately for her, this was almost constantly.
These sentences fit together akwardly - the way it's written now makes it sound like Agnes was a dried husk constantly, not energetic.
Agnes seemed duplicit in this scheme
Wow, what? No where else do you use such high vernacular - in fact, the way you have Agnes's accent jump back and forth from being country-ish (dropping the "g's" everwhere) to city-ish makes me wonder where this scene is being set at all.
I'm guessing that's supposed to be "thought."
Jill's mind wasn't too clear on specifics. But what it did know, was that Cliff was a much better name than Tim.
No. Don't give the mind it's own being for just two lines - it comes off wrong, and is hard to read. Let Jill think what Jill's going to think. More on that now:
*Jill stared blankly, lost in thought. Tim's father's name was Cliff? *
Just previous to this, and previous to that, and, in fact, mostly the entire time, Jill's lost in thought. This little bit comes right after having a startling revelation based off of something Anges said - give us somehing different. Have Jill start at the name, or ANY action - her blankness is getting boring.
"I'd like a glass of wine. A large one. Whatever goes well with, uh," she gestured to her plate, "this." She didn't even know what she was eating anymore.
Anges just called it alfredo, and since you gave us the dialogue, I'm assuming Jill was hearing it, therefore implying that she should know what she's eating.
*She didn't have anything to do now except show up on that last day.
She wondered if Tim would notice, or, baring that, care if she didn't?*
Confusing set of sentences again. I find myself stumbling, asking "care if she didn't
what?" Clean it up a little, and that shouldn't happen.
"Why thank you. Just add it to her tab."
Who's speaking here? Speech tags are your friends.
*Jill overlooked Agnes' comment and the apparent lack of any relation between Japanese internment and grape-growing. *
Whoa, again. Just like the high vernacular, we have unnecessary comments from someone who's mind is far away on a different subject. Anges' comment holds well on its own - don't have Jill back it up with something that doesn't fit her character.
What if Tim had what?
Or - daily? Agnes might come over every day! Could she handle that?
Jill's never mentioned where the two might be living one day - why can't they just not live around Agnes? Jill's never said Tim's had a dependence on her, that he can't not live around her. Even if your character's drunk, it doesn't follow the rest of the story that she might think this. Also, it'd be funnier, and more dramatic, if the reader has to realize that Agnes might come over every day even if she has to make a two hour drive to do it, instead of just coming around the corner. Oh, and Agnes, even when talking about the pregancy earlier, never said anything about wanting Jill and Tim to have kids.
Cliff returned with the check. He smiled at them both, and asked, in his handsome, rugged way, if they had any room for desert.
"Dessert."
*"Yes, there is something wrong, Agnes. I don't want to marry Tim, I'm not yet drunk enough to drown you out, and Cliff here in the most handsome person on the planet," she stated, very matter-of-factly in her mind.
"Oh. Well, if that's how you feel, Jill, I can't argue." Agnes returned to her previous topic. *
What. Did she think it, or say it? If she thought it, then she never directly talked to Agnes, and therefore Agnes has no room to reply. If she said it out loud, we need more reaction from Agnes than a polite little snippet.
She didn't want to marry Tim, she hated him. He was always right. And not in that controlling, dominating, scary way. He simply was always doing the right thing at the right time. She hated how he smiled that smug little smile of his, his little lift to his step after sex, that his name was Tim at all.
WHAT. Throughout all this, the reader's been given a very pretty picture of Tim. No where has Jill even hinted that he acted like this at all! Okay, sure, she's drunk so maybe she might be exaggerating a little bit, and maybe she's just an unreliable narrator, but if this is actually how she's felt about Tim, and how you want the reader to feel about Tim, then we need more to back it up with.
She composed herself and uncorked the second bottle or white wine as she tottered for the exit.
Uncorked it with what? Did she have a corkscrew, or was it a twist-top?
*"Jill? What's wrong? Have you been drinking?" *
Who's speaking? She calls it "Tim," but give the reader more to go on. The ending is very very rushed, though it does make me want more, which is a good thing.
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Otherwise, you've got something there, even if it is kind of tired. Jill needs to be set up as an original idea more, instead of just the soon-to-be-wife who has second thoughts, and Agnes needs to be less stock - a gabby mother-in-law is old hat. You need to make it new.