Congrats! I want a tiel really bad. The only way to be sure of the sex of a bird is to get it DNA tested, but with tiels, females tend to have yellow markings on the underside of their wings. Males tend to be more vocal, and brighter colored (I think about the color). I think Lupe is a really cool name, and it could be a boy or girl name. PCB will probably have lots of info for you