If I follow the news story, which doesn't tell it in order, Kimberly had an explanation for using a different name - not wanting her mother to find her - but her mother found them anyway. So it seems he was aware of the Christina Brook name prior to her taking off with Evan. Which, to me, means he already knew what name she put down for herself on the birth certificate. We know from the story that his name went on the birth certificate.
We also know that at the time she was arrested she had to have a photo ID or drivers license that had the name of Christina Brook. Law enforcement doesn't just take any name and date of birth and say "okie doke!". She was released on her own recognizance and that wouldn't have happened unless law enforcement ID'ed her. So it would be helpful to know when she obtained that photo ID or drivers license.
As I mentioned before, when her mother did show up what name did she call Kimberly? That doesn't get mentioned in the story but it would be useful to know. I don't think she only used personal pronouns like she or her. If her mother called her anything but Melissa I would think Evan's father would be either confused or angry. So, in all of this, I can't help but think he knew that Melissa McKernan wasn't her name either at the time her mother shows up.
And thus, I don't think the Christina Brook persona was set up in order to take off with Evan because that persona was already known. It is possible it was something as simple as trying to avoid paying someone. Usually people involved with a birth want to get paid so they make sure they have identification and/or insurance of some kind (including Medicaid) under the same name. So that would mean that she might have set up the persona to carry out welfare fraud. But if that doesn't apply, I don't understand the motivation for the creation of Christina Brook since Melissa McKernan was still viable. I am trying to understand the motives and impetus for changing to a new persona. Encounters with law enforcement is probably the most likely cause. But seemingly there are others.
In the end she bolted from Virginia Beach in short order leaving her child behind and never looked back. She was running from something or she is a nut job.