A longer paddle may be needed due to the width of the kayak, in a similar vein to SOTs - I'd suggest an extra 10cm compared to the normal length for the given paddler's height.
Technique-wise there are two observations:
1) You can see her elbows are moving behind the shoulder line - this means she is paddling "arms only" and will tire quickly. Secondly it exposes the shoulders to risk of dislocation. She needs to rotate her body in order to get her stronger core muscles to assist. Being in a less restrictive SOT kayak than a sit-in, she should be able to rotate her whole body, not just the upper torso. She can pedal her legs to assist with this too. Her feet need to be braced against something to transfer power to the kayak.
2) She is holding the paddle too close to her body - this manifests with the paddle entering the water by her body and exiting some distance behind. It's not efficient and would cause turning in a short kayak. She needs to hold the paddle away from her so that her arms are straighter. This will then encourage her to use body rotation to propel the kayak.
In short - the first exercise she needs to do is to paddle with her arms (almost) straight, rotating her body in order to move the paddle.
Take a look at this video from 1:09 onwards: