If your daughter is going away to a party she will probably be away 2 nights, could see to the horses before she goes, then arrange for someone else, friends anyone and as I said split the cost. The same for the next day and she can check on them just to make sure its all ok when she comes home. I can understand her wanting to go to a party, I was in same position at that age and loved it when I had a chance to go out and shared babysitting with a friend. Worked well
Another attempt by Trump to end the war with Iran
World Class Museums - why are they free to everyone?

. Cat was my DD's before he came to me 18 months ago - that'll teach me to check with her before I plan anything (haven't been away in 18 months!!)