I agree with James.. consent is everything. Did you both discuss these kinds of things prior to marriage? This is why communication is so incredibly vital.. best to discuss all potential situations that might be hard or soft limits to avoid surprises down the road.. now you’re at a place where she’s wanting to further explore and you’ve some hesitancy.
Further learning material is probably going to be a useful tool but do some research before you just jump on any one resource..
Open the lines of communication and try to see where things are stemming from.. her desires and your hesitancy. I would think if the relationship is mutually loving that she would be willing to at least open dialog and try to sort things out, out of mutual respect for one another. Level of control in the dynamic may also play a part.. relationships can fluctuate so long as both parties feel safe and their needs are met (to whatever degree your dynamic allows).