I think Castro would be a perfect pick, hes 40 years old. Co, NV, NM are on the horizon and Clinton already does good in OH, Latinos are the growing number of SEIU union membership, ethnic minorities. I think, since she cant pick a sitting senator and Kaine and Hickenlooper are too old, Castro would be best. Chris Murphy doesnt help her.
First of all, there are plenty of young potential VP picks. Murphy, Schatz, Heinrich, Booker, and Gillibrand are all under 50. New Mexico is not a swing state, Nevada is lean Democratic even without Castro, and Colorado can be won without Latinos. And she can definitely pick a sitting Democratic senator with a Democratic governor.