Bella has the gift of mentally shielding herself(she already had that when she was mortal, though) and others from any power that works within the mind. Mind readers, illusionists, etc. Anything that involves getting inside the mind.
Bella gets the power of protecting her mind and others by a speical non visable sheild, so no one can read her thoughts, or get in her head or others that she has under her sheild at the time.