Mary decided she couldn't risk anyone finding her in her current condition, especially John. Who knows what he would do if he realized she had just wanted to use Max for her own ends. But what could she do about it? John would eventually start to get worried and come snooping around. She had to act before that happened, and find some way to turn back into a regular human by that point.
Mary hurriedly began sorting through the vials she had swiped as her fingers grew even stubbier. Sitting uncomfortably on the tile floor, she could feel her rear legs shifting slowly, but she could not bring herself to examine the changes. She was more concerned with finding a way out before she lost the ability to pick up the vials and pour them into her canine mouth.
"Damn it," Mary cursed through her tears, her long tongue getting in the way of her words, and her long muzzle impeding her speech. Examining the vials she had managed to grab, Mary felt her heart drop with each vial. She had scooped up a completely random selection of vials, and she knew the one vial that would help her beyond a doubt, the "human" vial, still lay empty on the carpet outside. The vials she did bring into the bathroom, however, did not look promising. In fact, it almost seemed like the vials she had with her would not make anything better, but could make it worse. Nevertheless, they were the only recourse she had, and in the end she made a desperate decision.