The steady right-wing pressure to maintain maximum harshness against
convicted criminals seizes on and magnifies any outlying case.
Every decision about policies in dealing with crime is a probabilistic
one. If you replace policy A with policy B, there will be cases where
the result of B is better and cases where the result of B is worse.
Whether B is a change for the better overall depends on the frequency
of better and worse outcomes.
A wave of indignation is not a substitute for a rational evaluation of.
the results of using policy B, not even in one specific case. We
don't know yet whether convict Tubbs will commit more crimes after
experiencing juvenile hall than she would have committed after a
sentence in adult prison. Indeed, the general experience with adult
prison suggests it often directs prisoners toward a life of crime.
If B turns out to give worse results in a identifiable subset
of cases, that doesn't necessary imply that going back to A is
the best change. Maybe some variant B' would be better than
either A or B in such cases.
So I think that Gascon's latest decision was premature.