Paulina is a teenage mouse from Peru who is one of the members of the Thea Sisters.
Not much is known about her early life (other than her parents disappearing for an unknown reason), but before she went on to continue her studies at Mouseford Academy, she lived with her sister, Maria, back in Peru. She had a close friend back in her school days named Antonio de Moreno who runs a chocolate factory in Quito, Ecuador and sells them by the brand of "Cocoa Loco". They both lost contact as years passed by. As she arrives on Whale Island, she is befriended with four other mouselings; Pamela, Nicky, Colette, and Violet.
Paulina has grey fur and black eyes. Her hair is dark blue and tied in one long braid. Her main outfit is a long orange dress with dark grey pants. As the book series continued, she is shown wearing casual; a two-tone double layered orange shirt and a pair of what seems to be grey jeans as seen in The Chocolate Sabotage.
- Like the other four Thea Sisters, Paulina's illustration art in her intro at the beginning of every Thea Stilton book has been altered after being cartooni-fied.
- In later books after receiving alterations in her illustrations, she and the other Thea Sisters tails are missing.
- In the book The Legend of the Fire Flowers, Paulina's surfboard is orange and yellow color and blue for the image of ancient birds.
- In the book The Ice Treasure, Paulina and Nicky had developed a crush on Ashvin, creating a rivalry between them both, even though both of them are really close to each other.
- In the book The Dragon's Code, it was revealed that Paulina, along with Nicky, are in an organization called "The Green Mice".
- Despite being nicknamed Polly, it is rarely seen that the other Thea Sisters call her by that name. However, in the Journey to Atlantis, the other Thea Sisters have been seen calling her Pauly, an obvious alteration of the original nickname.
- In "Thea Stilton and the Secret City", Paulina reveals that her parents went missing for an unknown reason, making her the only Thea Sister whose parents' statuses are M.I.A..
- In The Frozen Fiasco, Paulina is revealed to be a big fan of mystery writer Vígmar Ratsson.