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, 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 yet to be 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 Nicky's closest friend is Paulina.
- In the book "The Prince's Emerald", 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.
- In "Thea Stilton and the Secret City", Paulina reveals that her parents died in an adventure in the Amazon Rainforest, making her the only Thea Sister whose parents are deceased.
- In "The Frozen Fiasco", Paulina is revealed to be a big fan of mystery writer Vígmar Ratsson.