Well, she's an Empath not a Telepath.
It's a mixed bag when it comes to what her powers can really do. She's able to communicate to Riker's mind in the pilot and with her mother numerous times. Even that one Betazoid stated that Ferengi have "minds we can't read".
I think when the creators gave Troi these powers for the purpose of making her useful in a unique way, they realized that having such such a useful ability would render most situations resolved. So after the pilot episode, her powers were toned down significantly and any situation that the writers didn't want resolved, they just threw in some techbabble like jargon that renders her powers useless.
Reminds of one of the pre-production memos from "The Making of Star Trek": originally GR proposed that landing parties have some sort of combadge that would allow them to remotely trigger the transporter when the shit hit the fan. To paraphrase one of the responders: you take the hazard out of the situation and you take the fun out!
I see the same problem with Q.