[@MiddleEarthRoze]I was thinking that they got caught in a tractor beam and brought aboard, like the Falcon.  Maybe they even arrived about the same time, but since Sheppard was so much better in a fight, they get to her before Han, Luke, and Chewie, and actually fight their way out.  Then the two ships could join up and head to Yavin.

Meeting the Enterprise would work as well, though I don't think they would have a reason to join the rebellion at that point.

I wonder how the rebellion would respond to EDI?  I could see C3PO getting confused with whether to treat her as a droid or a person.