There were several options. She could attempt Apparition, but she wasn't sure she would manage not to Splinch herself. The Knight Bus was no longer safe for a warrior of the Light, so that was out. The creation and use of Portkeys were highly regulated by the Ministry, so she and Aberforth hadn't been able to create one prior to the mission and she certainly couldn't make one then. Even if the Floo system weren't also incredibly unsafe for her, there wasn't exactly a fireplace anywhere nearby. She was in the middle of the woods, after all.