Johanna once was addicted to morphling. Maybe "addicted" is a strong word, but she liked how it made her feel, calming her and taking away the constant pain from all the injuries she sustained in the Quarter Quell that the Capitol didn't heal. That and the little burns that stung along her temples, where they put the electrodes to shock her. The morphling helped take her away. She would sneak some of Katniss' into her IV. Johanna didn't want to end up like the morphling addicts she saw, dazed and confused or strung out and shaking.
So when she saw this girl-- more like, when she ran into this girl, she knew what was up. Johanna didn't move when the girl walked towards her-- Johanna didn't move out of people's ways. They collided and the sorry didn't sound good enough for her.