[If you mind spoilers, please scroll away.]
What if Monika really just wants everyone to be happy? I mean all the advice she gives is valid, such as making sayori love you might get her killed, and if you ignore her warning on staying away from yuri she kills herself, so what if Monika is just a psychic and she know what is going to happen and shes really just trying to watch out for everyone while at the same time trying to get you to like her and forget the others?