When disaster struck, the people of Storybrooke were probably more prepared than most. They'd dealt with numerous curses and evil villains before, so when this one hit, they were quick to act.
The townspeople split into groups, dividing themselves between different parts of Storybrooke. Regina, for instance, stuck with Emma, Henry, Hook, and the Charmings, keeping between the loft, the Sheriff's Station, and the Mayor's office. Her vault was used as a place to research how to stop this invasion, and Granny's was a food outpost. The groups still collaborated together, of course, but everyone figured that a grouping system would be safer for everybody.
While trying to figure out how to stop this curse, Regina had discovered that she needed some sort of magical herb that was apparently somewhere out in the forest surrounding Storybrooke. And, the Mayor being as stubborn as she was, had decided to go out searching alone. Emma had tried to come along, but Regina insisted she stayed with Henry.
So, armed with her magic, Regina ventured out into the forest. It was crawling with the cursed zombie-like creatures, but she was skilled enough to either avoid them, or take them down quietly. Eventually, she found the herb she was looking for. She harvested it as quickly as she could, tucking it gently into her pocket. But when Regina turned to leave, she found herself outnumbered by zombies. A fireball sparked at her hands, but even she knew this was too much for her alone to deal with. And that was when an arrow pierced through the head of the zombie nearest to her.
Regina looked on in shock as the creature fell, seemingly dead. And then it was followed by others, arrows sinking into their heads. Before she even had a chance to see who was firing them, you had ran over, bow in one hand, and clasped her hand with the other. Without saying a word, Regina ran with you, getting away from the horde that had gathered around them.