That episode was lovely,

Mitsuri, the Love Hashira, had so many scenes that made me laugh.
From the scene were she couldn't help but laugh at the headbutt scene, to the point where she was being pushed to the ground by accident from the Sound Hashira.

My guess is her reaction is to blast past the guy torturing her and try to protect Tanjiro, only to stop at the edge where the sun is.
I'd go even further and say she wouldn't stop, but I'm not sure if she'd instantly combust then.
That would certainly proof her dedication to protect and set it above everything else, even human blood/food.
From what I understood, that lower moon guy Rui tortured his sisters or mother by exposing them to sunlight.