She thought her feelings were somehow NOT completely and totally obvious? Also, how much you wanna bet she was reading some mushy romance manga?
I mean she IS a former tsuntsuntsudere. Normal MC will never be able to through the act without heavy outside help.
...So you got someone you like then, Nee-chan?Does it look that way to you...?!You've gotta be kidding me?!Was I really makin' that kind of face?!Wh-what should I doooo!?D-...Hey, Nee-chan.Read manga in your own room, would you...Awww... I'll leave once I finish this one...*Roll*Ugh~*Pomf*Sp... Spring has come for Nee-chan...?!SHOCK*Floomp*