In episode 116 after Ultear lost the fight with Gray, she tells him that he cannot beat Hades, but does not tell him anything about Hades' weakness (eg: his heart).
This seems weird since when she had Zeref a couple episodes back, she was about to stab Hades in the back and take Zeref for her own purposes. This would imply that she was no longer on Hades' side.
Later we see that the guards knew that the room Hades' was in was something they could not lose control of.
Since the guards knew about this wouldn't Ultear know this as too, seeing as she was pretty much raised by Hades?