Mary's no bad guy! She just was in a tough fight then mercilessly beat her opponent once she gained the upper hand and didn't stop until she was too exhausted to beat her some... Yeah, that sounds a lot worse when I say it out loud.

Also, yeah, I'm pretty sure if Mary just said SHAZAM twice, her costume would be restored and the mud would be gone. She's a little too giddy right now from mercilessly beating.... oh, she's terrible!