As Elena's Sword of Catastrophe was still not completely ready, the move that she used was not a proper one. It did have a foundation of a move but that foundation still needed some polish and only then she could finally start building the move.
Elena obviously had many other sword moves in her arsenal that she could have used to fight the now strengthened Roger. So why was she taking such a dangerous risk by using a semi finished move like this ?
The reason behind Elena's decision is actually very simple. She had found the current time to be the perfect one to quickly solidify the foundation of this new technique of hers.
As currently both Lost Wanderer and Last Samurai were using quite a bit of their power, the amount of pressure that she was facing was insane. But at the same time, as Elena was not the only target of this pressure, she was still not overwhelmed by it. So this was just the right amount pressure to assist her in her growth.
