With EAD Matthews' backing her, Sonia dared to fight the entire security detail arranged at the McSuile family's Treasure Lake resort alone, and she was holding her own against them all until the high-tiers showed up. Even though she only did that to impress her new boss, someone like that would not be afraid to fight a newly awakened curse master to death.
However, it was a different story if one were to factor in Sonia's pride. Unless it was absolutely necessary, she didn't want to take that step because she only started this to show Ace that she, too, could hurt him if she chose to and had no intention of actually killing Lyra, as that would be akin to awakening the sleeping beast.
Yes, many of her guildmates had died, but there were still many alive, along with her father. She knew better than to achieve revenge for the fallen at the expense of the living.
