From Muppet Wiki

Desiree Casado (born 1985) plays Gabi on Sesame Street. She joined the cast in 1993, taking over the role from Sonia Manzano's real-life daughter.

Official bio (from sesameworkshop.org):

Desiree Casado (Gabi) is now in her 12th season with Sesame Street. Desiree plays the daughter of Maria and Luis. Her film credits include I Like it Like That, for which she was cast after her very first audition at the age of seven. Other films that followed were Bed of Roses, Joe's Apartment, Wishful Thinking and Gloria. She has also appeared in various commercials. Desiree loves to dance, especially Hip Hop, and is currently taking Ballet. Last summer she was featured in her first starring role in the independent film Juicy.