I don't think that follows at all. Kaoru is married, dedicated to Reiichii (or thinks she is), and Uta is the "little sister" and underage. That provides plenty of mental barriers to thinking about anyone else, let alone Uta. Or to 'realizing' what her attachment to Uta is actually based on.
I see what you mean. But none of that could be seen as 'leads' or cues to classify Kaoru as bisexual, or to even generate a speculation that she is.
That provides plenty of mental barriers to thinking about anyone else, let alone Uta.
Regardless. For a person to realize 'mental barriers' in connection to romantic or sexual attraction, she has to be conscious of those. Right now, what the author gives us is Kaoru being conscious to opening herself to self-love and independence so she wouldn't hurt either herself, Reichi, or Uta. I admit though, it's impossible to separate this "awakening" to Uta's declaration of romantic/sexual love for Kaoru, ESPECIALLY when Uta pulled herself away from Kaoru's family.
Personally, when the confession came in, in the chapters that followed, I find that the author's attempts to show Kaoru's mental process of the confession aftermath was kind of... inadequate, I guess? I just can't find any meat to support the case that Kaoru suddenly found herself wishing for Uta's presence beyond the need for psychological support (i.e wanting romantic/sexual connection with Uta).
We can only speculate. The frustration about this thing is what made me wish half-jokingly that Kaoru would snap GAY and have a threesome with Uta and Risako.