>>280514232
Probably a luck check similar to Gae Bolg. Shirou notes Hrunting had:
>aimboot
>and was perfectly lined with her and Shirou himself in the trajectory
She dodged by a sheer miracle because overcoming the impossible was natural for her. It worked as slightly diverting Hrunting's path.
They do note even after getting further diverted by breaking Shirou's 4-layered Rho Aius it'd still curve back and kill them though if Archer was alive to keep aiming.