This is Chara we're talking about. She is smart, logical, and deadly. She's already dead, so technically, she's immortal now too. Her hate is also impenetrable. Her only weakness is her human self. She's still innocent deep down, as Glitchtale showed. Chara is literally unkillable right now, from a logical sense of immortality. I understand the kind of power the Ghast has. Chara is in her weakest state, and already almost as powerful.
Give her her strongest form, and, well, the only one that could hope to oppose her would be one with the equivalent of seven human souls, as portrayed in Glitchtale. And even then, Ariel still had trouble. Only because of his past with her, and the help of the souls to take away her power, did he win that fight.
And while we're talking about Glitchtale, it's a safe bet that Chara is even more powerful than Betty. Chara handled Gaster like he was nothing. Betty strained against him until her Rhabdophobia trick.