I did not find Kreia TOO hard, she was difficult, but with lots of verpine prototype shields, and the trusty master speed/master flurry combo, from a level 26 weapon master, (who had the superior two weapon fighting III and the maximum increase damage thing) she fell fairly easily..... It was those lightsabres at the end that were harder, but even so, a high level weapon master / guardian should beat her without much problem.
To be honest, i found her about as hard as i found master Vrook on Dantooine when i was asentinel (if you are not a prestige he is HARD, much harder than the other Jedi - master flurry and master heal means he just rinses you very quickly, and he gets critical hits alot...)