"Olga" is kind of a mechanism, actually. She's (for the most part, aside from the knowledge of the peculiar drives technology) a technologically-imposed, almost airtight (she can't break character, and it's solid enough to thwart psionic snooping) alias for Melissa. That said, she wasn't supposed to be that!
The original objective (of the ANNIC NOVA AI) was to get Melissa's body on board the Pegasus as the equivalent of a "'Guest' Clone" -- installing an identity into a clone other than the prime body's original one -- a personality that is either generally compliant, modified, or completely generated from scratch. Legally, such individuals are viewed in a range from legally incompetetent to indentured servants (Remember, in the Third Imperium, slavery is illegal... except, yeah.). The problem was that the clone body already had a complete copy of the actual Melissa's identity already installed, and you can't do a permanent identity install into a body that already has an identity in it, due to limits on how the identity wafer game mechanic works.
So, as it stood then, Melissa was a "'Relict' Clone" -- essentially, a complete "spare Melissa on ice" rather than just a "spare Melissa's body on ice". Legally, a full person... except that she hadn't been logged as such, and the techs were supposed to turn the body into a guest clone technician for the Pegasus and they had a deadline to meet. Thus, they went the Personality Overlay Device route: re-mapping Melissa's memories so she was convinced she was actually Olga (and adding the peculiar variant of Engineering skill for good measure). Not particularly ethical, but it got the job done.
Now, the Annic Ai didn't really understand all these details, but had hijacked the authority/credentials that had been used to get Melissa Prime through her extraction from Feri/Regina, body mods to disguise her, and then get her onto the crew of the Silver Streak. It used them to revive the Melissa clone -- since it recognized her as a crew member -- and get her reprogrammed for use as crew for the Pegasus. (As I said, it's kind of sentimental like that).
Annic Ai thought Olga was "close enough" to being Melissa for its purposes, and didn't care otherwise. Two or so clone medical/psych techs realize that Olga is an overlay onto Melissa, but ain't going to say nothin. Everyone else (Mike, Director Kehoe, and so forth) thought it was some anonymous but powerful official, repurposing Melissa's vacant clone body as a walking decoy while the real, modified Melissa left on the Silver Streak. Mike thought Olga was "real enough" to respect as an individual (which, objectively, she was -- albeit, very un-self-aware by conditioning) and not just a meat robot.
The thing I hadn't covered, due to the limited space available in the short story format, was the reason Melissa's personality had already been installed in the clone.
