I think she means working both fronts and back at the same time, each would require its own yarn. I don't see how markers would make any difference in how many balls of yarn are needed. Working each piece separately would keep from needing multiple balls. I'm lost with the gap between yarns.
Cheating is an option. . . . Cheaters never win and winners never cheat, but smart knitters who want to retain an iota of sanity do, cheerfully. ~~Kory Stamper