I know it's very difficult to say no but you really must in this case. You're certainly not being unreasonable, if anyone is having to take a day off work, it should be she and definitely not you! We're both semi retired and have our 2 GSs quite often - at the moment, it's 8am Monday to 5pm Tuesday as our son is working abroad all of August & our DIL works Monday to Thursday. It's hard work as they're 5 and 10 and chalk & cheese so there's a lot of refereeing ! In term team we collect them once a week, feed them & take them home at bedtime. If we have other plans like holidays, we just say no to having the boys, we don't feel taken for granted that way and, as we're only 2 miles away, we tend to be asked frequently for last minute baby sitting. If we're available, we'll do it. Your case is distinctly different, I think your daughter has got a nerve, frankly!