Hard for me not to be a bit overprotective of Dak at this particular scenario because I'm reminded of a similar scenario that went badly... 
Isilmewen reasons that the bird returning or not confers about the same information either way, so stays her bow at this point. But you can bet that if it shows up again without some sort of missive that she'll be ready to shoot it then. "Once may be coincidence, but twice? Twice is not chance."
Either way, her proposal is an indirect routing, to track and follow without being directly on their path. It might offer more safety in obscuring our group's movements to any adversaries expecting us to follow their steps exactly, but will take longer to get to our destination, wherever that may end up being.
To make sure they're on course, Isilmewen offers to be the one to go back and forth to check the trail.