The randomness there really gets me down. She's a major character, she really should keep to a more regulated schedule to make her less inconvenient to access. There's really no reason why she shouldn't. As a great man once said, "Deliberately annoying is still annoying."
There is no randomness (that goes for the entire game. There isn't even a random number generator in my code), but her schedule is deliberately hard to decipher. This is modeled after the Persona games, which tend to work in a similar way. The idea is to make it hard for the player to plan too much ahead. I want the player to have to break off his plans once in a while because an unexpected opportunity popped up. This will show up more often once I implement the feature where girls may move about the town to a limited degree. Like in Persona, you're not meant to be able to focus exclusively on one girl all the time. The game forces you to spread your attention a bit if you don't want to waste actions.