Lordy, lordy, puppha! I feel for you.
First, I echo the opinion that you should not have more kids. To heck with what others want you to do, if you think it would be wrong. I knew a woman who was constantly pressured to have another kids, because her husband and whole family wanted a boy. She was digging in her heals last I heard (fingers crossed she still is). Another woman that I met not long ago - a mother who brings her daughter to the same dance class as my kids - told me that she wasn't sure about having another kid, but that it was really important to her husband. I couldn't help but point out that she wasn't obliged to have kid just for that reason, and that I would not be willing to do it.
One family had seven girls - more than they could afford to support - all because one of the parents wanted a boy (probably the father, since this was a chinese family). What good did it do the mother and kids?
In my own family, my wife has often expressed regret that we will not have more children, to which I tell her that I am not sorry and that I would never consent to have another one.
As it is, in my family we have two kids, a Buddhist and a fundamentalist Christian. Things get pretty tense at time, but I have long ago stopped caring if I say something that runs counter to her beliefs. This isn't to say I show disrespect, but rather point out the other interpretations whenever that chance arises.
So, say my kid is sick, the wife prays, and a day and a half later the kid is well. Hallelujah! She talks about the miracle to the kid, I sit near and point out that I have also gotten better from illness without a single prayer.
It irks her sometimes, but I think the dynamic between us is such that we don't break into fist fights over it.
Of course, you wife has long sounded like she holds you in very low regard, while my wife thinks well of me in most respects. And honestly, I think it is lack of respect that is causing your woes more than anything else.
So, stand your ground, speak openly without being disrespectful (use your standard, not hers - for her just being non-born-again is disrespectful), and dont' have any more kids with her. Accept that the parent to whom you daughter is closest is the one that will most determine her beliefs and If that parent isn't you, then, well...