Keep in mind when analyzing Aika that she's just now beginning to confront and process her feelings toward Wataru. To this point, she hadn't the bandwidth to deal with her home situation and experience the sort of normal psychosocial development that would lead her to recognize romantic attraction (either in others or herself).
Even at this point, she couldn't put into words why she moves reflexively to keep other girls away from him, why she worries as much about his well-being as she does her precious sister's or why she feels so much more at peace with him than without him.
She's getting reeeeeeeally close, though...
I think your assessment is mostly accurate; however, it is only part of the larger picture. Aika's biggest issues are: her inability/unwillingness to introspect, rather than blindly following her emotions, as well as only viewing things from her own perspective. She comes across as being very self-absorbed, or even solipsistic.
This is exacerbated by the fact that she keeps interfering in his life, often in a very rude and sometimes violent manner, attempting to sabotage even the most passing of female acquaintances he makes. She is constantly throwing out mixed signals and confusing the hell out of the poor guy because she refuses to get her shit together. It's gotten to the point that even her best friend, Kei (whom treats her with kid gloves and is an ass to the MC at times as well), feels compelled to step-in and stop her from fucking things up any further.
And that is before you factor in all the bullshit the MC has to deal with on top of Natsukawa's antics: his abusive mother and older sister, said sister's weaksauce attempts at reconciliation, and her dragging him into the student council because apparently Little Miss Perfect and her harem of simps can't handle their responsibilities nor go about recruiting more members properly. Sure, that last part isn't Natsukawa's fault, but she isn't making things any better for him now, is she?