At the moment that's all we have on her, but I hear her name *a lot* when the game gets talked about (e.g. "Not as difficult as Talulah"/"Harder than Talulah") so I assume there's a lot more to her.
As for the anime itself, we got told she was sent to take control of the command tower, so even though we see her melt a building, then melt the rest in the plaza to trap the Rhodes Island team, we get to understand that she has a fair amount of self-control should she want to use it.
Mephisto is just bad writing.