Well I hate to say it, but the chances of finding a Raven with Stealth armor being sold on the market would be fairly unlikely. Anything of that nature would have been stripped for valuable parts and left for the wreckers to pick up the rest. It may be more likely that your character was able to drop a Raven in some sort of a trap. Maybe incapacitating the pilot when you brought a heavy flow of rocks down on his head with an explosion. Then you were able to dig out the Raven and escape with it before the rest of his lance mates showed up. Unfortunately, mechs of that nature are fairly rare, especially in the Republic of the Sphere days after the Jihad where Stone fought to stockpile or decommission the majority of the mech forces. The only reason that Allia has stealth armor on her Ghost is because she grew up on the planet where they made the mechs and the armor, and the mech was her grandfathers during the Jihad. Most mercenaries generally can only afford stock market mechs with little to no bling.
Please don't think I'm trying to downplay your ideas, but since you're not too familiar with the world, I want you to understand why this likely wouldn't make sense.
Not a problem, I appreciate the feedback!
How about this instead:
Dishonored, distraught, de-citizened, she was left with very little in the way of options. Unable to afford a mech of her own, she instead started applying her tracking and survival skills to bounty work, bringing in the wanted for cash. It wasn't long before she managed a lucky break: a lance of bounty hunters specializing in taking down the more heavily armored heads had an opening, their fourth, a Raven pilot, recently took a dirt nap and they needed to fill the spot. She got that spot and so spent several good years with the merc-group.
The luck didn't last. On the trail of pirate with a locust, the group followed him into a canyon... where an ambush waited. Pinned in the canyon, being fired from above the canyon walls, the target had called in some friends. She and her lance mates did their best to survive but it wasn't long before she was the only one left standing. As a last ditch effort she emptied her salvos into the canyon walls and ran, giving her dead comrades a burial, along with their attackers.
The loss was crushing. The group had lost its leader and most of its fighting force. The remaining work crew, dropship crew, and sole mech pilot divided the remaining assets and disbanded, leading up to her seeking to join the Black Sun Company.
Such a scenario makes a stealth mech a lot easier to operate since damage from bounty hunting would be lower than that from straight up battle, half the time she'd probably not even take the targets in mechs but rather in bars. Working as a bounty hunter, she'd be able to plan her attack to her advantage and make major use of her mech's stealth capabilities to take down the target. It also plays to the strengths I intended her to have while also giving her a chance to prove her metal post-dishonoring.
Lastly, the scenario also plays better to a Raven II, if that's what you think I should field? I'm still not sure how the height of the raven II would compare to a Raven. I can't find height values so I can't see if the Raven II is less stealthy than its lighter counter part. 5 tons isn't that much in mechs, but small to medium is a category change that may bring with it issues. I'd really like more info from you regarding how the mechs compare.