我很喜歡你呀 in a specific context
"我很喜欢你" has the almost same usage with "I like you" in English, depending on the scenario, could be treated as "I love you" but again, it's rare. 

In daily case, we(native Chinese) rarely use(or used?) this sentence because comparing to the western people, Chinese usually are regarded as a group people who are shy, barely express emotion orally.  

But in this case, the author seems like depicture a little girl who has a crush on her brother. It's unethical but also natural considering their age. And it's far from incest since it's just an emotional activity.