On her way to know what Noah wanted to discuss with Nicki, Ariana happened to cross paths with Diana instead, who came looking for her. Due to that, she couldn't meet up with Nicki and Noah and missed out on everything they talked about.
After Diana was gone, she still planned to go after Nicki, however, when she noticed she was coming back, Ariana swiftly ran into Luna's lunge and pretended like she wasn't up to anything.
And Nicki, who expected her to follow behind when Noah escorted her out of the Luna's Lounge to discuss Nadia, was surprised to find out she chose to stay behind instead.
She was on the bed and appeared to be reading a certain book. It was kind of weird to her at first because Ariana definitely would have followed behind due to the kind of signals she kept getting from her before Noah decided that they go somewhere else to discuss.