The ball was in Kūkaku's court, and so when she threw it back, she threw it back but good.
She'd painstakingly
gotten her supplies and went to her workshop to carefully blend the right chemicals and gunpowder to have her rigged nicotine patches do what she wanted them to do. Once they interacted with the chemistry of Sherlock's skin, boom! Not enough, of course, to turn him into another armless wonder, but definitely enough to singe the cavern-cheeked bastard.
Checking every step for any other booby traps, Kūkaku slipped into Sherlock's office and padded over to his desk. First, switch out one pack with another, made to look used but not enough that he wouldn't clearly notice that it had been switched out.
And then switch out the patches elsewhere. Maybe if he though it was just the pack she rigged, he wouldn't even suspect the actual patches.
Mwa ha ha. She was enjoying this game far more than she'd ever allow herself to admit.
[[ Establishy! That Kūkaku was in Sherlock's office is okay for broadcast, but not the details, please! And office totally violated with permission! ]]