Answer: The character is Sagisawa Fumika from Idolmaster: Cinderella Girls. However, searching simple tags of the image on Gelbooru, like her name, "book", and "smile" doesn't seem to get the image. So, it might only be on Pixiv, Twitter, or some other art platform. Google and Yandex couldn't get the source, either. Perhaps give it a search on a booru yourself or try Pixiv with her tag, 鷺沢文香. Or hope that someone else can find it.
Answer: already search all page on danbooru use her name. got this image from here https://twitter.com/banko003
Answer: Ah, sorry then. Didn't know you already knew her name. Perhaps try messaging the person from Twitter and hope they know the source and didn't just find the crop somewhere.
Answer: I don't think i can message her. nah don't need to sorry. And thanks for the help