She did not directly cause the people's deaths, Reina was under the impression that Aria had the power to kill it right away.
But to kill the dragon, Aria actually calculated everything, with the help of her own senses and Alena's power, along with her charged up strikes. If it wasn't for the people who died, and the rest who continuously attacked, Aria's power alone wasn't enough.
However, she was too tired to explain to Reina.
Aria had to admit, she was someone who could jump ships very fast. At this rate, mixing with Reina, who had the qualities of a potential savior complex might just hurt her in the future.
If Reina turns out to be a dangerous ally, then she wanted to eradicate the relationship before it was too late.
"Alena, let us go. We have to discuss more important things, and I am also tired after was. ting. all. my. po. wer." Aria enunciated her point, pressing hard on the individual syllables.