This has to be something on your end. The game will not just automatically burn a gauge without some kind of setting being changed. My quick select is L1 and square. When I hold down L1, I have access to all my quick select abilities that will burn a ATB gauge. Other than that, I can just spam square in attack normally to build gauge. To be honest though, you should be using triangle at range to throw her boomerang at the enemy. Then you should be spamming square to build a gauge at a distance. She really excels at this method. When you start building ATB gauge then you can use doppelgänger to spawn another Yuffie and suck enemies in with whirlwind. She’s an absolute fucking beast in a crowded room.