Then you’ve done all you can do. I’d just consider yourself lucky it only got one plant. A lot of people swear by UC roots, just bleach is so much cheaper and does the same thing.
IDK what else it could be. Sudden wilting like that from an otherwise healthy plant…there’s really only one likely culprit. Fusarium or root rot, and it’s rarely fusarium. Especially in winter indoors with no other plants around. Are these clones or seed plants?