So, checking her design and USS Washington, she's basically Washington's Abyssal form?
Uhhh so purifying her turns her into an adult....
What the hell is going in?
Given that this Abyssal is the boss fight for the "PQ-17 Convoy" map which the historical USS Washington horribly, horribly botched; I think that this is something of a reference to how, earlier on, Washington did not have a lot of accolades to her name and only a massive regret. A more in-universe explanation would be that the Abyssals locked away her later memories in order to make her more pliable to their cause.