Since it's still hotly debated as to whether the whole sister thing even existed at the time ESB was filmed, I think you have to leave ROTJ out of the equation. Luke also tried calling to Ben first.

It might also be a "one way call" scenario. Leia senses Luke, but can't send a message as Vader does. Luke obviously couldn't call Han, (could he sense Han was frozen?) didn't know Lando, and I've no idea if you can telepathically call a Wookiee. It might also help if you're sending to the one person who's probably also thinking about you at the time.

Did the term "Force Sensitive" exist prior to the prequels?