In 1.5 hours, she got 43 cups of water (assuming they're all full)
So, in an hour, she got 43 : 1.5 = 86/3 cups
From 4 in the afternoon to 3:30pm next day, that is 23 hours 30 minutes. (full day - 30 min)
Convert 23 hours 30 minutes to 23.5 hours
So, she will tell you that 86/3 x 23.5 = 2021/3 cups of water is gonna be wasted. (if you need to round it's 674 cups.)