I have to agree with Davy -- the moving stuff is going to be located in the state's code and not in the individual's decree.
The individual won't need a family care plan because she is married, period. It doesn't matter to the military if that spouse is a biological parent or a step-parent -- retired military here and that's how it was during the 20 years I was on active duty.
Now -- back to the moving issue, jurisidiction, and stuff.
If the bio-dad to the child did not leave the original jurisdiction (Maryland), then even if the mother moves with the child (around the world), Maryland will retain jurisdiction until the father moves out of the area. (IMHO -- I am no attorney, k?!)
If Mom has a signed contract to enter the military in January, here's what I suggest.
1. File now to get permission from the courts to "move in conjuction with your military career" and use that signed contract as your "significant change in circumstances" to justify going back to court.
2. Work with dad on coming to an agreement for a long distance plan.
Personally -- and again I'm no attorney -- since Mom has had custody, since dad has previously agreed to a move either through court or his actions, I think the court will let Mom move.
I also suggest that as the child gets older, as the time with dad goes well without incident, that Mom consider more frequent and longer periods of time with dad -- particularly if dad asks.
And Mom, hire an awesome attorney. Once you leave, you will be on active duty and the SSCRA will protect you some, but not totally, from going back to court. So -- do the right thing, ask now, get the ball rolling now, and if this isn't settled by the time you leave, make 100% sure your attorney knows how to contact you and what you want and stuff. You may be able to appear by phone to get this solved.