The OP knew that she was bringing food for that many people and beverages for her family - she didn't know that she'd have to do her own cooking, take food to Lakehouse Sally's, then help cook there for an upspecified period of time, then help serve, help cleanup, and then go home to do her own cleanup (if it hadn't been done before they left). I think she was complaining about Lakehouse Sally getting more work & "help" time from her on top of the work she'd already done at her own house.
Lakehouse Sally apparently has a history of always needing more help and never showing up early or sticking around to "help" if the event is not at her house. She does the minimum and expects other people to "help" her when she doesn't return the favor. Except by hosting another time and expecting more help...
edited to add - I used to arrange to swap my help with a friend, we'd spend an afternoon with both of us working at their house (sweep, mop, vacuum, dust, move the couch & dining room table to clean under them - that sort of thing). About the third time I helped someone and they...were too busy to help me in turn, I quit doing that. At all. Once is an coincidence, twice is indicative of *something* going on, and the third time was just the last time.
I help relatives that I'm staying with or people that I'm close enough to that I don't mind and I don't do more than I feel comfortable doing. But I'm never again swapping my time & energy for their help. At least in part because I'm almost 60, I'm hypothyroid, and I just don't have the energy any longer - but in part because...I just don't think that it's likely to happen.
At least one time, every time we set up for it to happen - she got called to pick up a kid from school, she got sick, the car broke down, I got a job as a substitute teacher, it just never, ever worked out. But if even the universe is against me getting help...well, I quit arguing with the universe.