Well the idea is that Hanayo had about 110% trust in Nico before; she was always insisting that they smile/not give into Monokuma/etc, and so when she’s placed between a rock and a hard place here, of believing in Nozomi or Nico, despite the fact that Nico blamed her a bit earlier on, that could easily be written of as technically she was suspicious in that manner and she can’t really blame her. The real fact of the matter boiled down to who would the person, in this case Hanayo, want to believe is the killer? No matter what you say, it’s definitely easier for Hanayo to just believe that Nozomi is the killer; everything was laid out cut and dry and it would all make sense, and Nico is still the all smile’s senpai, ‘let’s do our best guys’. On the other hand, if Hanayo were to believe that Nico were the killer at this point, she’s going to say the person who gave her hope after Rin’s death fell to the same path and she’d really rather not believe that. Not only that, but Maki is supporting Nico, and, after Maki solved the trial last time, it’s easy for Hanayo to trust in her/that she has the right idea when she’s unsure herself.Hopefully that little rambling made sense. It’s more so the last few sentences that explain it, really, but ah well. In short: Maki supports Nico so it’s easy to support them as Hanayo obviously places her trust in them; it’s easier on her mental state to believe Nozomi was the killer, out of revenge for Eli, then to believe Nico, who was all anti-despair pro-hope earlier, killed Honoka for money.