I'd take aware her control and power by blowing her off. She insists she can "name" the baby whatever she wants? Well no, of course she can't. She can stomp around proclaiming "I name thee (whatever)!" all she likes but that doesn't make it true. Noting official will have the name listed, it's just something she can do in her head and you can't stop her from that so disengage. Roll your eyes and say "Mom, you can think her name is Daffy Duck for all I care, but you will address her as (name you've chosen) or (consequence you're comfortable with." Then be prepared to follow through because you know she'll push.
Not only do I fully agree with this, I would take it a step further. This isn't just a naming boundary being crossed. There's an implication that a religious one might be, as well. Like you say, OP, this is stomping on your religious beliefs.
It's common in here when there are problems with a husband's mom for people to respond it's his job to control his
mother. I'm a little surprised there isn't more of that in these responses, because it's a 2 way street. Your DH needs to see that any intrusion by your mom, with even the appearance of major boundary violations, needs to be nipped in the bud...by you.
That's why I like JenJay's comment about consequences. And it's probably even more important with the religious portion of this. If you can't be polite but firm in person, send an email. But make it clear that all major parenting choices will be made by you and your DH.