Sleepover?

So my sister planned a sleepover for Saturday night. She doesn't get off work till 7 p.m. and she has to be at work by 7 a.m. the next morning, so she said that everyone can stay at her house when she leaves. What the hell kind of sleepover is that? Why invite people to stay over if you're not gonna be home? Besides that we're expected to bring sleeping bags or something since she does not have enough beds for everyone. I'll come over for a bit Saturday evening, but I'm going home to sleep in my own bed. 🙄