I am not sure that there is an Evan. Maybe there. I found two divorce cases involving two of her aliases. It appears she married in Arizona under the Melissa Mckernan alias and became Melissa Losey. However, it appears that the Losey divorce was in 1995 and then perhaps there was a remarriage after that and another divorce in 2001 with a decree in 2002.
This case in 2001, you will note upon seeing has a case type of "Family Court without Children"
Family Court Case Information - Case History
This is the Divorce case involving Losey from 1995. Also no mention of children.
Family Court Case Information - Case History
So, if what her mother says had any truth to it - her source is Kimberly after all - that would mean that this alleged child named Evan would be alive in 1998. But that would mean that such a child would either have to have been fathered by someone other than her husband or from prior to 1995 at a minimum. If that were the case it would explain the divorce without children. But at the same time would contradict her mother's claim that Kimberly changed her name to go to Virginia Beach since all of this is taking place in Arizona in this time frame.
Naturally, not much of this is going to end up making sense because there is almost zero chance that Kimberly's mother has any idea who or what her daughter is.