Not only do we pick the kids up at 7:30 (after waiting in the car at 7:10, when we told her we'd be there at 7!), but they get in the car and immediately start begging for food because "they didn't have time to get dinner."
The whole freaking point of her keeping them till 7, is so that she could enjoy dinner with them.

So we get home at 8:00 and not only do they need to eat dinner, but they also need to shower and bedtime is 8:30.
I know it's not the end of the world if they don't go to bed at exactly 8:30, but it's a routine that we have established, and a schedule that works for our family and it should be respected. She even said when we dropped them off "so you'll pick them up between 7 and 8 on Sunday?" I said, "no, at 7 because they are still in school for two more weeks and have to get ready for school/bed".
Gosh, I swear she does this crap to work on my nerves. It has to be intentional. I would never drop them off to her at 7:30 at night without them having had dinner. Heck, even when we drop them off at 5, we tell her in advance that they haven't eaten yet.