If I had to guess why Chiyu did what she did, then
Either way, her reasons will probably be selfish, even if she states that they are for the better. Well, regardless, Haru would not have gotten his ability back just by beating Nomi. There has to be a better plot way for him to regain it.
Also, why didn't Lime Bell's energy gauge show up for the fighters in the contest? She just popped out of nowhere, with full special gauge, to do her deed.