Characters Played: [OU] Sephiroth
Can Sheba read your character's mind? Yes, but only when he allows her to or if he's injured/maimed etc enough not to be able to stop her.
Will your character be able to tell? Yes.
What sort of mental defenses will Sheba encounter? We've been there before ICly but generally Sephiroth's mental defenses are impenetrable and kept that way. However once 'let inside' these walls her presence there would be kept in a strong bubble in order to shield her from information that he doesn't want her to know.
How deep would you like Sheba to be able to go? If she pushed while being let inside of his mind Sephiroth would probably push her out and never let her see again. That being said, it would be interesting for perhaps one day (CR permitting) for her to be allowed to know more about him this way - or conversely cos I'm terrible he could be made, by way of physical injury to open things up for her to see.
If Sheba were to use Reveal and your character was within the area of effect, would she notice anything she wouldn't see normally? Going to pass on this one.