As for the young lady, I am pretty sure (based on procedure) she was asked if she had anything on her before they searched her during the booking procedure. [...] By not admitting it she holds full responsibility for the charge.
I get this. But at the same time, if she exercises her right to remain silent, that should not lead to charges that are more serious than they would have been outside custody; for such a situation to occur
de facto removes the "right" to remain silent, because it increases a penalty as a result of standing mute.
If she
denied having anything, thus waiving her right to shut her cake hole, and
then was found with stuff, that's another story entirely. Then I would agree with you that she bears full responsibility.
But if she stood mute, then the only charge she
should be subject to is the charge she'd have been hit with if they'd found it on her in the initial search.