Maybe she got home for 8:30 as she knew she would have to get something to eat, and have a shower before going to bed.
I think you need to think about wedding meals, I was invited with my young son months old, we were sat on a table, near the food, we were starving, as there was only little bits to eat after the ceremony, which had been about dinner time, so we didn't have any dinner, then the reception was late getting stared, think 7, with nothing much to eat since breakfast. The odd thing was, the tables were supposed to go up in order, I didn't know, so had gone up as soon as the said the buffet was open, not so much for me, but for a rather grumpy baby, who was hungry, there wasn't a lot that he would want to eat, bride was Indian, I managed to get a bit of what a little one might eat, but that's when I was told I should have waited. 🤔 But our table was last, yet they knew that's where the baby would be sitting, I would have fetched some jars of baby food, if I had realised there was anything to eat for several hours. After we had eaten, it was getting on for 9 pm. They hadn't even done the cake, but I had a grumpy child and a drunk partner. He had been sat on a table with a load of strangers, which he did like (socail anxiety) plus hours of no food and alcohol, don't mix. So we returned to the accommodation. Both child and partner were sick in the night. I think the spicy food sat well with my son, but it didn't help eating late at night.
I don't blame her leaving earlier, if it's running late and service is going slow, so probably thought if I go now, I can get something to eat at home before having to go to bed.
With people saying she should have got time off, how do you she didn't and got it rejected. She probably wasn't expecting it to run late, or expected food to be served earlier. I had thought the food at the wedding I was attending, would be for 6 or maybe earlier, as the wedding was at 12pm so she maybe thought she could have food and then leave after. The Mil, shouldn't have been so fussed if the bride was OK with it.