User blog comment:Omega natsu2/Episode 193: Seven Dragons, Review./@comment-24729244-20140802090402/@comment-7418318-20140802090850

No.

Even if Minerva could see and hear Mavis, she would have been too far away from her to actually hear her.

More likely Minerva figured this power of feelings out from seeing Natsu in action several times and giving several nakama speeches of his own.

Maybe she also read a book about it, but dismissed it before, until she saw evidence with her own eyes.