Darn it. I've never cared for the "Una" thing. We know that "Number One" is a generic term of address for first officers, also used by Picard for Riker, Georgiou for Burnham, and Lorca for Saru. So the fan theory that "Number One" was her actual name and that "Una" was a nickname derived from it was either naive or contrived, and it doesn't work for me at all. I prefer to think of her as Robbins, her name in Early Voyages.
Well, from the way Pike used it, maybe he was addressing her by her first name. Although EV established her first name as something beginning with "Eure--" (probably Eureka).