The technique that Aelina used is a secret technique that is part of the foundation of the Battle Maiden Sect. It's a technique that all the higher-ups of the Sect must learn and is part of why nobody can learn anything about them despite the number of wars and battles they've had throughout history.
It's a technique that lets one create an 'avatar' or a clone, but it's a little more complicated than that.
The technique itself isn't about creating avatars and is just one of its many uses. However, for what Aelina tends to do, all she needs is the clone in front of her.
After filling the 'clone' up with Qi, Aelina had it put on some clothes along with a veil to hide its face, then waved her hand and sent it into the pocket space where the Crimson Slayer Sect's headquarters is located.
