For background, I work part time, DP works full time, we have 2 DC age 2.5 & 4 and life is pretty hectic at the minute.
It has become like an unorganised arrangement that DPs half sister (9) comes most nights for dinner, comes to our house at the weekend etc... and it is just getting too much.
My DC like playing with her sometimes but she can be incredibly bossy with them and my eldest daughter doesn't like it. She will over ride my parenting, is the best way to describe it, for example if DC leave their dinner I will say "its ok, we can try again later" and lets call her S, will say "no, I will feed you your dinner" and continue to shove a spoon in DC face no matter how politely I ask her not to.
We can only let the dog in the garden if the gate is shut, she will open the back door without asking and twice now the dog has got out. Again, I've politely reminded her and asked her not to without checking the gate is actually shut but nothing changes.
She wanted DD (4) to play a game of play pretend which involved a 'cheating boyfriend' so I reminded her of DDs age and that it isn't really appropriate to play like that with her.
I asked S and my DC not to go in our bedroom as we had Xmas presents on top of the wardrobe not yet hidden, DC can't open the door. S opened it then said she didn't mean to, but she would have no reason to be near the door. There has been numerous times she has took toys off DD to make her cry so she can comfort her.
She has put hairspray on DD when I asked her not to which resulted it in getting in DDs eyes
Although it is nice to have S round and let all the children play together it is so hard when DC just don't want to play with her and she is going against everything I ask her not to do.
I haven't had a reply yet but I text MIL along the lines of we don't mind watching S for you but it is always at short notice and with our own stresses of work etc, we are struggling, perhaps DC could come to you sometimes or we could go out somewhere instead.
DP is on the same page as me, I just hope MIL understands.