That would be bad, as it would potentially risk dragging it out to tomorrow or even longer depending on how long Schultz would drag it out for and how stubborn she would be. Best to rip off the bandage now.
And look at the Tweet Trump posted from earlier, before that latest bit came out:
https://twitter.com/realDonaldTrump/status/757335224397225984
No matter what she did, Trump was going to attack her for it:
-She completely ditched Schultz: Clinton wasn't being loyal to a longtime ally and is a person who's willing to stab anyone in the back.
-She dos what she actually did and gives Shultz an honorary position: Also bad optics, just in a completely different way.
There was no good option for Clinton here. No matter what she did with Schultz, Trump and the Republicans were going to pounce on this one way or the other. Thus, that being the case, the best decision would be whatever makes this go away the fastest, which seems to have been to give Schultz an honorary, worthless position so that she steps down as chair.