Sorry in advance, this is a long one.
My sister and I were extremely close growing up, however we drifted when she met her ex and have only recently become close again after they split up. She has a 3 (almost 4) year old daughter.
In the past when DS has asked me to babysit, I've struggled with DN behaviour. She doesn't listen to anything or anyone, she will have a screaming fit when asked to do anything, my dogs are petrified of her and have to be kept away from her because she's grabbed at them and dived on them in the past, she's constantly diving on and off the furniture with no caution for whether she may hurt herself and as awful as it is to say, is just generally difficult. I've mentioned it in passing my DS but not wanting to fall out again, haven't pushed.
Last weekend DS asked if she could come over and stay the weekend with me and my DD6. I agreed as I thought it would be nice for the girls to spend some time together. It was absolute mayhem. I cooked a meal DS said that DN would eat, she took a single bite and didn't touch the rest, got up and left the table to play. I told DN she would need to return as our house rules are noone leaves the table until everyone is finished, she had a tantrum and DS said it was easier to leave her be so off she went whilst my DD ate her tea. DN then returned for dessert which DS gave happily, my DD raised that we only do dessert if you finish your meal, DS again said its easier to just let her be. There was the usual commotion of her trashing the toy room and refusing to tidy, trying to get to my dogs in a seperate room and having a fit when told no until DS all but demanded to take her in to see them and using my living room furniture as a trampoline.
Come bedtime, DN is put into the spare bed in my DDs room. For almost 20 minutes she was up and down, throwing things at my DD to wake her up, she ripped DDs heads of her favourite squishy toys and was repeatedly shouting to DS that she needed to go to bed or she won't sleep. I told DS she needed to do something as it wasn't fair on my DD. She moved her into the spare room where she was sleeping and it continued with DS telling her to go to sleep and her causing mayhem.
So my question is, what do I do next time this is suggested? I've tried putting it off but she just asks a few days later. I have worked with children with Adhd in the past and I honestly think it's a possibility, but I don't want to argue with DS if I suggest it.
I love DN so much but I honestly cannot deal with her behaviour and I'm now dreading the next time I'm asked to babysit.