She is married to the father but is not herself the mother of the child. That automatically makes her the stepmother by definition. See Webster's definition of stepmother.
Unfortunately, Webster's doesn't make law.
The OP married a guy in prison for rape. She wants to play mother to a child she hasn't met. She is calling most of you out for disagreeing with her flawed assessment of law. (and me next).
She raises points about the case that should have been raised at trial or in the post-trial motions if we can believe her statements. There is an appeals process. I'll note that the number of inmates that say they did it is very low. And the number of inmates that say their public defender sucked is very high. The correlation between personal responsibility and prison incarceration is very low. Huh? I wonder if that is connected?
They could save his VA money to hire the best attorney they can get. Paying child support would be admirable in any other situation. He isn't going to see the child while he is in custody. Best to work on what can be changed.
TD
** Edited to account for the qualified help comments:
OP: Hiring an attorney or contacting the local Innocence project is your best bet.