I've always had the impression that C-3PO and R2-D2 were one step above "stow-aways" on the Tantive IV. When we are introduced to them, they are wandering the hallways without much direction or purpose (as far as I can tell). It seems to me that R2 happens to walk down the wrong/right corridor at the wrong/right time and runs into Leia who is desperate for a place to stash the DS plans.

Given the prequels- either as they exist or how they could exist... and given that the Skywalker and Organa families most likely have history with this pair of droids... Does this change your interpretation of those events? Are the droids specifically hers? 3PO seems pretty ignorant of "The Princess" when Luke and Ben are watching the holo.