It's like taking 1 picture of multiple things, rather than tracking all of them at once. At that range, the bullets trajectory isn't an issue, Jolyne, just has to protect herself instinctually w/ her stand, as seen previously in her fight w/ Pucci. Remembering all of the bullets as they are, is akin to remembering all the separate layers in photoshop while editing, whereas remembering the reflection is compressing them all to a single layer/ rendering.