It’s Bruno Mars’ Sister, Presley!
That lovely lady you saw before is Bruno Mars' little sis, Presley Hernandez! Side note: Hernandez is Bruno's birth surname as well, and his legal first name name is Peter, after his father.
The Hernandez clan is actually quite large, with Bruno and Presley having four other siblings, including three sisters (Jaime, Tiara and Tahiti) and a brother (Eric). Bruno, Presley and their other siblings grew up with music in their homeland of Waikiki, as their dad Peter and mother Bernie were both professional musicians and exposed their children to a variety of music at a young age -- Bruno even performed as the world's youngest Elvis Presley impersonator when he was only 4 years old, and we're pretty sure Presley was named after the King too.
Nowadays, while Presley's big brother is winning Grammys and topping the charts, she and her three sisters have formed their own musical group called the Lylas! Maybe Bruno and the Smeezingtons can lend them some of their songwriting abilities. He already seems like the greatest big bro ever -- ahem, please see the Louis Vuitton wristlet he gave Presley as a gift! -- so we wouldn't be surprised if he did do everything he could to help launch their careers.