Grrr.
I am am being unreasonable I think, and so is she. Basically, she offered ages ago to babysit for my birthday. I never go out, had my first drink since xmas in May!
Most of all I was looking forward to the lie in the next day. And I knew I would have a great time out cos I could relax and not worry about having to get up with kids next day (they are 2 and 3, very much early risers).
My own mum had offered to babysit a few months ago, but she lives over an hour away, and MIL only 5 mins I arranged for MIL to do it. She was round earlier today and casually said 'oh I think we'd better do it here, only I've got my plant in the cupboard, and it's so close to being ready be a shame to spoil it now!'
You know what kind of plant I'm talking about right? Anyway, I don't have any moral issues with her doing that. Actually, can't she just lock the cupboard then they can stay over? (that's where I think you lot will say I'm being unreasonable).
But I just feel like it's ruined my birthday. 
I am probably being over dramatic, but it's so annoyed me.