I will quote a couple of rules...but not to bash you about them!
There are two different rules that might apply here. One is the Look Back Rule. If the Look Back was in effect (ball in circle) the runner may not: Leave a base once she is stopped on it; Stand still in one spot while off the base; Stop twice between bases, or; Reverse direction a second time.
You titled this post "Leaving Base Early". That is actually a different rule and a different violation. That rule involves a runner taking her lead off as a pitch is released. The rule says that the runner is out if she "fails to keep contact with the base...until the ball leaves the pitcher's hand".
Which rule applies depends on what point of game action is taking place. The Look Back is designed for when there are active runners and the ball first comes back into the circle. The "Leaving Early Rule" is for when the pitcher is in position to pitch and making her delvery.
I don't really consider anything this runner did as a violation of the spirit or intent of the Look Back Rule, which was designed for the sole purpose of ending delays in the game by the runner playing "cat and mouse" games with the pitcher.
It's not really a "leaving early" violation...except in the strictest technical sense that this runner may have momentarily "lost contact" with the base. She wasn't doing this as any sort of attempt to advance to the next base- and, apparently, not when the pitcher was actually throwing a pitch.
Could an umpire call this minor technical violation and support the call with the written rule? Yes. Should he make this call with respect to the spirit or intent of why these rules are in the book? I would say...NO!
It can be a slippery slope when an umpire starts basing his calls on the "spirit and intent" of a rule, instead of how the rule is actually written. That can lead to personal opinion being inserted into a call. And not every umpire is going to know the spirit and intent behind every single rule in the rule book. But these are two particular rules where I believe most trained and experienced umpires would agree: Minor technical violations of these rules that are not related to a player trying advance to the next base or gain an unintended advantage can be ignored.
We have an acronym for making a call like this: OOO. That stands for "Overly-Officious Officiating"!