There's some evidence to suggest that women don't benefit from carb loading like men do. I just eat normally in the days leading up to a big ride and limit myself to food that I know aren't going to bother my stomach. For sure, I stay well hydrated in the days leading up to a century. I start the morning of the ride off with a big glass of water. It means more frequent bathroom stops, especially that morning, but it's worth it. I, personally,
drink more frequently than every 20 minutes on a century. I try to do a 3:1 ratio of water to an electrolyte/calorie replacement drink. To encourage sufficient calorie intake, I put a bag of bite size food (often Paydays) in my top tube bag. That makes it easier for me to grab a bite while I'm pedaling. If I wait until set stops to eat, I'm often in a hole.