Invited DD1s friend over for a play date in half term, and we were expecting her at 10. At 11.30 there was still no sign, so I sent mum a text asking if friend was still coming. Mum said yes, but could she now stay the night as something had come up and she didn't have anyone else to ask.
Her DD has never been here before, but DD1 likes her so I said yes, no problem, ad generally I am happy to help people in a bind, though I was a bit 
that she was happy to leave her DD with people she's never met overnight.
Friend came, the girls had a great time and we're good as gold. All good. Roll on for friend to be collected, and the mother texts to say she'll be over at 8 now not 6 - ok fine, no problem for me, and girls are happy.
This is where I'm not sure if being a cow or of mum is BU. 10 mins after leaving here she asks if I can have her DD overnight this Monday , as again something had come up- I said ok and hadher DD from after school mon and dropped her at school this morning, thinking that was the end of the matter. Only it wasn't - she's just text me and asked for me to have her again after school and overnight tomorrow.
I've said no. I might be being unreasonable, because technically there isn't really any reason why she can't come, I just feel a bit of a habit forming and don't want to fall into that trap. No actual reasons have been given for the need for me to have her, just 'something has come up'.
Her DD is lovely, but DD2 is in teething hell and when she's staying over I'm anxious the crying might leave her tired for school, so find it difficult to relax, and my DD doesn't sleep as well as she's not used to sharing a room, which is absolutely fine for the occasional night but I really don't want her knackered come the end of the week as we are away for the weekend and it'll be crap if she's grumpy.
Please tell me I'm not being horrible and that you would have said no too?! 