The visitor to the sheriff’s office wore her hair in a ponytail tied with a pink scrunchie. With a matching pink top, dark jeans, and black boots, Sienna Casas, 4, was a fashionista – apropos for someone who has performed on the gabfest/variety TV show “Ellen,” hosted by comedian Ellen DeGeneres. That’s right. Sienna is a budding diva. And she has her father, Orange County Sheriff’s Department Deputy Nick Casas, to thank for that. Since March 2019, Casas, who has been singing and playing guitar since he was 10, has been posting videos of him and his daughter performing songs…