This is my theory only:
I do think that she was wrong on her assumption about the force bond at first. No matter how intelligent you are, it is normal to be wrong in your assumption.
Also I do think that over time that Kreia learned that it wasn't so. I have a theory that she had a deathwish and manipulated the Jedi Exile to believing it and getting to the Malchor 5 and forcing her to fight Kreia on her terms.
It was implied in one of her conversation that the 3 Sith Lords deserve to die because if they won't be stopped they would ruin the entire galaxy.
it was implied in the cut content with Lonna Vash, When someone switch alignments and other reasons, A force bond can be weaken. I do think that by following to dark side, Kreia weaken the force bond a great deal. Due to the unnaturalness of the force bond, I do think that Kreia saved the Jedi Exile by going to the Dark side.