To understand what happened earlier we must look things from Aster's point of view, since the enemies couldn't react fast enough to see the incredible example of agility and maneuverability that Lina displayed a second ago.
She not only never stopped slashing the barrier created by that girl from the Fireheart, but despite the shield users successfully increasing the range of their defense by adding intent to their shields, at the last second before the barrier shattered, the sister in the middle didn't stop her charge.
Instead of that, she followed through with her attack which was naturally blocked by the intent and fire cladded shield, and then without a fraction of a second of delay found an opening in the defensive wall created by those two and used the momentum to propel herself upwards, successfully bypassing the shield users to then appear in front of the girl from the Fireheart.
