For me it sound like more that she don´t want that anyone getting the PN to reach the Raftel as Roger did and she don´t screw up again as against Roger. In my opinion this isn´t much clear, but seeing how Oda build up Roger character, I can´t imagine he making off such move without fighting off Big mom. Luffy must do the way because he didn´t come back to Totland and also he must save Sanji, for Rogers case he don´t fear Whitebeard. So he fighting off Big mom while Oden copie the Red PN is still a possibly.