This. Just because they have a certain ability, that doesn't mean it's "activated" all the time. It's like carrying a flashlight around; you have to actually turn it on to use it.
I don't know? From looking at the transcript for "The Loss", I get the idea it is always on. She may not consciously choose to notice other minds, like we try not to listen to others conversations, but it is still always there. We can't switch our hearing or sight or smell off. I don't believe she can turn a sense off.