Big oof when she told those people and she heard her say the stuff about being nothing but an annoying childhood friend.
I don't think she meant it negative kind of annoying, but more like referring to her habit of helping and I guess it can be a bit of nagging, as you could see Raika would point things of her appearance that Atori had to fix. Ahaha. Meddlesome people are probably her type.
Anyways series seems interesting so far, I like this author, their couples are always very sweet.
My read, is Atori very much likes Raika, and potentially wants her all to herself and/or is worried that if Raika gets too popular she'll leave Atori behind.
Like you said, the "meddlesome" adjective specifically is pretty accurate to Raika; she's always going out of her way to help others (and we know the reason from Raika's internal monologue), and she specifically is always fussing over Atori.
My initial thought was that she was trying to downplay Raika to the other two, in order to ...I guess make her seem less desirable to others so that they wouldn't take Raika away from her? I don't think that's likely to be the case anymore, and instead I think Atori is just unable to be honest with herself about her feelings for Raika, and thus can't be honest about how she feels about her when talking to other people. But Atori had eschewed acting/performing in front of others all this time because it was enough for her that Raika was watching. That's not what you do if you see your childhood friend as "meddlesome / annoying".
And, Atori gets fully into the role of whatever bit of acting she's doing, becoming another person entirely, it would seem. So a sense of confidence and issues with self-image might be at play--and there's plenty of precedent across manga for characters to deny or even miss their feelings for someone out of a sense of "not being deserving", or whathaveyou. If she's got self-image/self-confidence issues, and she knows how well-liked Raika is, she might feel like she "can't" act on her feelings toward Raika.
Which mirrors Raika's hesitance to do the same. They're seemingly born out of different rationale, but the two instances of "one-sided love" would then also make sense for both characters in their respective ways.