It's not so much the shadow length she cares about but the fact that things seem to be changing while they walk which it wasn't before. Or at least she thinks it wasn't, it's hard to tell in this heat but either way it does help her feel a little encouraged that they are on the right path.

"So I'm going to go out on a limb here and guess that like me, you're having a hard time remembering things about yourself right?"