My DD2 has a good friend and they often go out locally together and do sleepover at each other's houses. The other girl often won't take a "no" from her own mother and often organises herself and makes her own arrangements. She is a lovely girl and a good friend however.
I explained to my DD yesterday that her and friend could spend today together, leaving Tue for a general bedroom sort out and to find a clean selection of clothes and pack a bag for a few days away when we're off to visit grandparents. I did say no sleepover Mon night as Tues will be a busy day, with lots of little jobs to do.
Friend has suggested my DD sleep there, but I said no to that too as 1) she'll be tired, grumpy and useless at thinking on Tues ( not what I need) 2) she will wander about locally all day with this friend and I'll have to have the hassle of enforcing collection arrangements with grumpiness from them both!
Also when they've spent all day together before, there's always a small incident, last time a small group of boys in their class arrived on the park and my DD got bashed on the head with a football in a bag! I know it isn't this girl's fault but things always escalate and two friends together turns into a big event and neither then want to fine home.
So AIBU in saying to DD's friend
No, sorry, that just doesn't fit in with our plans for the next two days. Another time, perhaps?
She said to me
It doesn't take all day to pack a bag!
Was rather surprised by her reply!!