I think she doesn't even get that Tsubomi is calling her a siscon in the first place.
This is pointless.But when it comes to your sister, your eyes glitter like I've never seen!When I'm talking, you always act so bored!Ehh!?Moron!You're only making it worse!That's why you're important to me!that you're really cute, just like my sister!I'm just saying,Tsu!Wait a minute!Wa-Ahhh!I'm leaving.If you love your sister so much, why don't you go out with her then!?All you've been talking about is your little sister!