~chuckle~ The Colonel's reaction is covered in the beginning of the Talisker saga, the first parts are up, and I am currently working on it.
As for Virote Isamu, I haven't written her back story, or fully fleshed her out in my writing, but here's the basic outline. The Colonel did indeed interview her. Her record in the Arena was well known, and showed her to be MechWarrior of talent. What is only alluded to, however, was her former service in the Draconis Combine Mustered Soldiery, where, as a woman she was marginalized, ultimately driving her to leave the service of the Dragon and strike out on her own, ultimately ending up on the Mercenary Star.
In addition, Sigil owns a 10% stake in the 69th as a founding member, and there is a gentleman's agreement that allows the founding members to recruit, for the most part, as they see fit. So, ultimately, the Colonel's interview was pro forma.
While I'm on the topic, I will also mention that Captain Weddle and Lt. Hamilton have a simmering dislike of her because of her heritage. Having grown up fighting against the Combine, they are rather mystified that Sigil would recruit one, especially given the Dragon killed his older brother James.
Sigil, however, feels responsible for dispossessing her when he destroyed Samba, her Vindicator, and almost killing her at the same time. In his heart, he knows it could have, perhaps should have, been him instead.