I don't know how likely that is. Her telepathic powers didn't pick up the Picard imposter in Allegiance, for example. I don't recall whether she was ever around the coalescent organism in Aquiel or Admiral Quinn in Conspiracy, but if she was and failed to detect the aliens in question that would further indicate the unlikelihood of her picking up the Thing's malevolent thoughts. However, that's not to say that if she deliberately probed for such thoughts she wouldn't find them.Skylon wrote:Troi may be helpful (I know, I know....*GASP* and *LOL*) in this situation as she could likely sense any malevolent thoughts by the Thing, and of course the crew can always count on Data not being the Thing.
The only other examples I can think of would be her inability to determine whether the Romulan in The Defector was being honest or to pick up the Romulan spy in Data's Day, but that could simply indicate that people from a species with telepathic potential can be trained to block Troi andothers like her out. The Thing probably wouldn't have that advantage.
If the Thing got a hold of anyone such as LaForge or Crusher who knew of Data's off-switch, neutralizing him would be as easy as it was for the subverted Crusher in The Game.