I'm starting to think she got rid of the child, for financial reasons.
The other two kids, being military dependants, bring in income.
Lisa did not. They actually had to pay for Lisa's healthcare, there was no extra payment from the military for her.
Money seems to be an issue with her; a divorce doesn't cost hardly anything, if it's uncontested. There's a certain level of immorality in DB's entire life. I don't see her being more upstanding in the care of her child(ren).
AND....if she was enthralled by other cases, she may have seen some parents as "heroes", and thought she could attain that status. Maybe speak out (like John Walsh), or be seen as a victim (getting donations, etc).