Many (or some) Jedi seem to have the idea that the Force has some kind of a will and a desire to keep itself in balance - hence the whole prophecy referring to Anakin needing to balance the Force, Qui-Gon believing that the Force somehow deliberately created him, etc. Lots of fans seem to interpret this whole "balance of the Force" deal as though imbalance means "too much light side or too much dark side in the galaxy at any time," which I think is erroneous. There is nothing in the movies themselves to support that the Force works this way, with two sides constantly in conflict with each other that both need to be kept at bay, as though the Force is a set of metaphysical scales - I think it's important to note that the phrase "light side" never appears in the films; and that the reason for that is that the Jedi (at least as Lucas envisioned them) look at the universe in the sense that "there is the Force, and when it is misused, corrupted as it manifests in people and places, that is the dark side, the imbalance," not "there is the light side and the dark side, equals and opposites."
As for Kreia herself: keep in mind that she is a control freak, a self-determinist, and also that she used to be a respected Jedi Master, and then the lord of all the Sith. I think it's more than likely that she picked up the idea of the Force having a will during those experiences and was never able to shake it. She probably looked at history (being a Jedi historian) and saw that repeatedly, light-siders and dark-siders have been in war after war, and with the revelation of more Sith being out in the Unknown Regions, that suggests to her that there's no end to the conflicts in sight.
I think that, no matter how much Kreia may have ever wanted to believe that everyone can choose their own destiny or whatever, she was never able to convince herself that the Force is not putting up the Jedi and Sith to their activities. It's also more than likely that the fact that both orders cast her out in shame and disgrace colored her perceptions of the Force in general. Hence her hatred of the Force: the Jedi and Sith both rejected her, and she can't un-see the patterns she's seen. To her, it appears that these Force-users are just going to be endlessly fighting, and so many innocents are going to be destroyed because of their wars, and everyone will lose in the end.
Erroneous? Most likely. I don't see why the Force would need to keep itself alive by fueling these conflicts (or want to especially if it doesn't have to), but it's not hard to see why Kreia would come to that conclusion. Just another example of the completely accidental genius of TSL.
And yes, Kreia's pretty much definitely insane, or at least a major-league hypocrite (which she indirectly admits to if you ask her why she uses the Force if she hates it so much). For all the things about the Jedi and Sith that she claims to revile, she's pretty much the same as them, playing the same game, with the only major difference being that she hates the game itself, too.
"Grant Allen [...] had written a book about the Evolution of the Idea of God. [...] it would be much more interesting if God wrote a book about the evolution of the idea of Grant Allen." ~ G. K. Chesterton, The Everlasting Man