Stella's magic came down like a hammer against Twilight, who only had time to make a shield out of her spell. It still cracked and almost shattered against the blow, but it at least absorbed most of the impact itself, leaving Twilight unharmed although strained. The strength of the blast still sent her downwards into the ground, leaving there the biggest crater the place had yet seen with her standing in the middle, her shield falling apart around her. As she looked up she saw not Stella firing again at her, but instead her extending her magic upwards to pluck Rainbow Dash out of the sky.
Twilight shot upwards, unnaturally sped up by a spell, and tackled Stella before she could finish what she'd started. Rainbow slipped out of her grasp as the two were carried skywards by Twilight's momentum, and she fell through the air, only caught by Pinkie and Fluttershy before crashing to the ground. One of her wings was bent at her side, unfit for flying in that state, but aside from a general roughing she hadn't sustained any other heavier injuries.
Far above, already past the clouds, Stella and Twilight wrangled with each other. The latter had encased herself into a magical barrier, and the way it burned Stella's coat where pressed against it had left a trail of smoke on their way up. Any spells that Stella had tried in the short time it had taken them to cover that distance had bounced off, but they had only been small and simple blasts. The next time she lit and released her horn, her spell spread out behind her instead, a wide round sigil glowing in the middle of the sky.
Twilight found herself suddenly stopped as she passed through it. It was almost like slamming into a wall, though the impact was on every part of her equally, her speed and acceleration instantly reduced to zero by the other's spell. It still was enough to daze her for a moment, only not knocking her out because of every other protective spell at work in and on her, and she lost hold on her barrier, which fizzled out.
Stella was on her in less than a second. She shot out a wave of magic and pure kinetic energy, hitting Twilight as hard as she could while there still was an opening. The alicorn went from floating motionless above the clouds to plummeting back first even faster than she'd climbed through the sky, so fast the air was slowing down her fall more than gravity was helping speed it up. Her body, still limp, was moments away from the ground when Stella teleported below her, already charging up another spell.
She fired at Twilight as their bodies were about to touch, a stream of energy large enough to envelope the mare whole. But it never hit its intended target. Stella only realised too late how Twilight had teleported, only when hit by Twilight's own equally powerful spell.