I think that Yuu is supposed to be in love, but the mangaka is deliberately not drawing attention to it to make it seem like she isn't, because her reaction to love is a lot more subdued than Touko's is. For example, saying she doesn't hate Touko kissing her, noticing Touko has lovely eyelashes as they're about to kiss, flinching in that small panel because of all the shoujo sparkles going on, saying she doesn't want anyone else but Touko to be in love with her, etc. However, in a way it's dismissed because it's accompanied with with a "but I'm not in love with you" in the narration, since it's from Yuu's PoV and she doesn't think she is. She's sort of tricking the readers using contextualisation; things that would normally be viewed as romantic suddenly aren't, purely because the narration frames them as platonic.
I think it's quite clever. You can see it again when there wasn't any glaring focus to Touko freaking out about the indirect kiss when they shared their drink, instead depicting it only as a panel of hesitation before drinking. Some of Touko's behaviours are also treated this way: her curiosity in Yuu's room, her going out of her way to seek Yuu out, etc. They're not explained in the narration because they don't need to be. They've been contextualised as romantic, so that's how the reader sees them.
I think the mangaka knows that drawing something is an active choice, so decides what she includes carefully. there's a lot from Yuu's side that isn't platonic, but the unreliable narrator mechanism is used well enough that it doesn't seem like there is. I think it's especially glaring when you compare the fact that she wanted to reject the dude who confessed to her beforehand, although she said they'd become close, and thus might be even more willing to endure his overtures in the same way she endures Touko's now. Despite that, she never made anywhere near an effort, and allowed Touko to pursue her from the start, whereas she intended to turn the dude down from the start.
Might just be projecting, of course! It's fun to think about, though.