Hikaru, your #3 is correct.

Mascot is very much a small person or a small foam covered "figure", being a mascot is a bit demeaning unless you are a small child and a fanatic for the subject. "ansWer"

"A poster girl" = on the advertising material. She stands and looks pretty. "A mascot" = she dresses up in a costume (maybe a banana costume) and dances around. You cheer the team she supports. "A spokesperson" = she is a representative. You will see her speaking about the product/business in the media.

Please anser => Please answer