Originally Posted by Heretic
Where is that explained in the movie?
What do you mean? They only found Shaw was because Xavier had located him through telepathy. Once Emma sensed another telepath, she immediately blocked Xavier out which is why Xavier tells The Man in Black that he is no longer able to help them. I'm referencing the comics when she is in her diamond form, Emma can't use telepathy therefore her block would have disappeared allowing Charles being able to sense Shaw. This is probably why she didn't shift into diamond form in order to keep her mental block up.
Diamond Emma = No telepathy
Human Emma = Keeping mental blocks up keeping Xavier from sensing them