At the very least, Agatha didn't start that fight. She fought back, after being (in her opinion) sentenced to death unjustly. They were literally trying to execute her, and it appears her tool for killing them was literally the magic they were using to try and kill her with, she just twisted it around on them somehow.
Much of her issue with Wanda also appears to be concern for the state of the Earth; she noticed a mega amount of magic being used, and showed up to figure out how. And when she realized Wanda was using chaos magic, that became a problem for her, because of the risks.
Honestly, other than the bit of gaslighting she did to amuse herself while hiding within the fantasy, Agatha really hasn't done anything evil. Particularly when she only just realized that Wanda's magic is actually creating things for real, at the end of this most recent episode; if they were just illusions and Wanda was deluding herself, then killing "Sparky" and torturing the "children" is just mucking about with someone's imaginary friends. It isn't real. Hard to consider that "evil" territory, either.