Maka is more resistant to hallucinations/mental manipulation than most--at least, it doesn't send her off into despair event horizon and in her home canon she could dispell illusions.

Obviously that's not happening here, but what happen is her seeing Medusa everywhere and telling herself over and over it's not real and she's not there. When SE characters are threatened, though, they tend to flare out their souls--and that's what Maka has been using as a means of defending herself against the shadows without her weapon partner. Without a specific target due to confusion, though, the light will be shining everywhere and all over the place. It won't hurt people that aren't shadows/super duper evil insane, it might even help with her other tactic of reassuring people that it's going to be all right, but it will tax Maka quite a lot.

...Shonen logic dictates that she'll still go on even when half-conscious but at the end of it all she's definitely going down for a long nap.