I've been getting quite hung up on the possible name mentioned - Rebecca/Becky Ochoa. Assuming that the women at the bar who provided this name were in fact talking about the correct woman, I do believe that this name has some thread of truth to it. I'm skeptical that Rebecca Ochoa was her actual legal full name since I feel that by now, especially with the trial of this murder, someone would have uncovered an unaccounted for woman by this name. Again, totally just my hunch. I do understand that paper trails and inter departmental communication was mostly terrible at that time so, it's entirely possible that this is her actual name and she has just fallen through the cracks somewhere - especially if she were an illegal migrant worker. There's also a handful of girls named Rebecca Ochoa listed in the California birth index (searched this at familysearch.org) during the possible birth years of this woman. I did a generous search of 1940-1960.
So, my hunches that I have been working on are that either her first or middle name was Rebecca/Rebekah/variation there of (in the above referenced search, I did find 2 or 3 woman with Rebecca listed as a middle name with the last name Ochoa). Ochoa may or may not be her legal last name. If it is not her legal last name, I'd suspect that it is the last name of her child/child's father, her mother's maiden name or the last name of an intimate partner.
As for "Shirley", I am thinking daughter, mother, or intimate partner. Following the leads I've mentioned above, that could mean in any of those cases the Shirley mentioned could be named Shirley Ochoa. I've found multiple women named Shirley Ochoa whose ages could fit any one of those scenarios. Unfortunately, looking at Facebook profiles, obituaries, etc for these Shirleys, I haven't found anything that jumps out as being linked to this woman.
I'm at a bit of a loss as to what Seattle would represent. The first thing that came to mind was perhaps an unofficial marriage in Seattle to a woman named Shirley? or perhaps they met there? Or as mentioned in a previous comment this could represent the birth place of a daughter named Shirley. The Seattle part kind of almost rules out Shirley being her mother's name because I just can't think of why you'd place Seattle in such a way on a tattoo for your mother. Although, one interesting note is that one of the obituaries for a Shirley Ochoa mentions that her family was a military family and they moved all over the country so. that did pique my interest a bit and would kind of make sense - as if Seattle was a special place they lived or something memorable happened there.
I apologize that this has been long, I've just been kind of thinking out loud and sharing some of the rabbit holes I've been exploring. I'm really hoping that this woman's family can get closure soon.