Shrimp and grits? Together? And looked forward to? Oh my. :eek:
Just tell her “No, you are stupid and boring.”
It might not be that bad in a small group of you, even if the people are annoying. Try and filter out “word” and “sweet” - you know what she means. Hope the conversations get round to something like films that anyone can talk about. IME most 4 people can manage a conversation for 2 hours.
Of course, I may be over-generous to her, but it’s worth trying to make the best of it. You never know.
Word.
I’ve been in similar situations before, and when I’d rather not go to a gathering I always find it awkward saying no because I don’t want to hurt people’s feelings. If I say I am busy and I can’t make it, I ALWAYS get the, “well, why can’t you come?”. I almost feel like saying, “I’m busy, that’s all you need to know, it’s rude to keep persisting that someone come if they don’t want to!” But of course I end up saying I have to help my grandparents with things, or some other made up scenario. Really, why would people keep persisting someone come to their gathering if they would rather not? If they’re forced to come they won’t have fun anyway, so just leave it at that. I know when people decline invitations to my gatherings I just nod and say “aww that’s too bad, maybe you can make it some other time”. 
Gary T and Turbo Dog, shrimp and grits is a terrific dish. The shrimp is savory and spicy and usually cooked with veggies and sausage, then served over grits. You may find that it helps to think of the grits as polenta. 
I like the decline with as little explanation as possible, although in this case I think I would add some longer term denial, as in “gee, thanks for thinking of me, but I have A LOT of family committments on weekends.” (to guard against her trying to reschedule for the next weekend).
Then, before she has a chance to jump on this, you might steer the conversation to a new area, by saying “During the week, I’m just so swamped with work, I’m sure you know how that is!” and then ramble on about how some project or another is kicking your ass and inviting her to babble for a little bit about her work week (I don’t you don’t want to hear about her work week, but think of it as a little investment to get her off the subject of weekend socializing).
Sadly, I do think you have to go to this party because you already accepted the invitation. If the date was more in the future, you could bow out more gracefully, but at this point, she’s probably already done the shopping and some of the work for a certain number of people.
Call her about 20 minutes after you were supposed to be there. Tell her you were on your way and the cops pulled you over. Tell her you didn’t have your license with you and they had a report of a stolen car with the same description as the car you are driving. Tell her you are under arrest, but you’re sure it will all be straightened out soon enough.
I did this to get out of a dinner at my boss’ house years ago. I’m sure he thought I was a lying idiot, but I did get out of the dinner. Obviously, this will not have any chance of succeeding if you are taking public transportation or walking, but it is brilliant advice in any case.