The character is Tenka Adachi (足立 甜花) from the visual novel / hentai animation Shoujo Ramune (小女ラムネ).
I've collected a few screenshots of her here.
For the image, I'd prefer the design to be more towards the VN's style with her giving a peace sign in an idol-like pose like she was posing for a photo.
Something similar to this, just with her being more confident / less shy.
Another example of a good expression would be this image.
I'm definitely not the best at explaining things so if you need more to go off of or have any other questions then feel free to ask away ^^