Mercury sees the thief get killed by her comrades- and immediately fall unto the Vulnerary he stole, breaking the vial and spilling it's contents on the ground. "Well, crap. I wanted to do that." The soldier's call catches her attention, and she sees the well dressed swordsman go around the corner.
An idea pops into her head, and Mercury backs up a bit for a running start- also taking care to keep an eye in Leon's direction for if he needs help. Any second now... While she braces, she swallows more of her drink.
Move to F6 and wait.