You know, it kind of makes sense that it would be Suwako who cursed Nitori if she held a grudge over that back in Maribel Quest. Did Kanako/Suwako know if Nitori associated with Utsuho during Okuu Quest?
They may have known that Utsuho worked for Nitori, but Nitori wasn't complicit in anything that Utusho did during that quest, either.
As for Suwako cursing Nitori, she did say that it might be worth reminding people of her existence, but don't you think that turning her into a hollow person who needs others to care for her is a little harsh? And moreover, kind of misses the point of reminding people of her existence, if no one is associating it with her. She also did say remind
them, not
her. I don't think her remark was directed at Nitori, but rather the world in general, who all tend to associate Kanako as the face of the shrine's divinity.
It also seems extremely likely that if Suwako were involved in this, Kanako would know enough to at least suspect her. Sanae said Kanako had no idea why the islands fell. That being said, it certainly wouldn't be beyond Kanako to withhold information from Sanae, either, but we'd have a hard time getting a chance to ask her in person, given what happened last time we tried.
Of course, the most singular argument against Suwako having cursed her is the fact that Hina is convinced she's not cursed. That alone seems pretty decisive.