As soon as Hachi finds herself the subject of Manon's observations, she moves to stand up straighter, hoping it will help her look a little less dishevelled than she fears she does at the moment. As per usual, in the face of such a well-styled and likeable person, she feels a little bit like Girl B overstaying her welcome in the background of the heroine's scene.
She's a little too caught up in Manon's effortless heft of the garbage bag next (So confident! Hachi is always half-worried the bag will rip and rain garbage down on her if she's not careful, though that's never actually happened) before she realizes Manon has now grabbed two bags to Hachi's zero, which is no good--especially when it's Hachi who should be doing all the work here for reasons she's decided on her own. She takes up the one bag at her side and sneakily moves to grab for the one Manon had just dropped, as well.
"H--eh?" After managing to toss one bag (she's sure not nearly so coolly as her upperclassman) into the incinerator, the other girl's compliment lands and Hachi turns to look at her, wide-eyed and face pink. "Oh, that's--'artfully tousled', gosh..." She runs a frantic hand through her curls again, her other hand grabbing tight to the remaining garbage bag, and releases a nervous little laugh. "I think that's definitely giving me too much credit, haha--but, thank you. That's really--nice of you to say. I mean..."
Here she takes a moment to gesture clumsily to Manon's own hair, as if to say 'Especially when yours looks so much nicer', before her hand drops back to join the other around the tie of the garbage bag, fidgeting around the twist of the plastic there.
"My hair used to be longer, but it was really hard to manage... it looks like you take really good care of yours, senpai, to keep it looking so pretty and healthy at that length. I really... admire that."
Wait, is that fine to say?! It doesn't sound like a backhanded compliment to say it looks like she has to take really good care of it, does it? It didn't, right? ...Did it?! Aaghhh... If Emi were here, she'd be able to tell her. (If Emi were here, she'd tell Hachi exactly where she went wrong, and in how many places--to help her, obviously. Just to help her.).