Fiona will always be absorbing low levels of kinetic energy and storing it within her body. The levels will be low enough to prevent any visual effect, and therefore no objects will slow or stop when near her. She can then utilise this energy to prevent herself from being immobilised by any means. She couldn't be held still by telekinesis, puppetry or any other physically manipulating ability, and she would also prove immune to paralysis induction, immobility and paralysis touch, as well as neurotoxins. The only way to prevent her from moving freely would either be to remove the kinetic energy, or to break her spine.