Well, think about it my dude:
Women are competitive af when it comes to looks. A big chunk of their self-esteem comes from it for more than understandable reasons, (which I don't intend to classify as good or bad, IMO it's just biology). Of course she's gonna feel jealous about some cuter, younger girl turning you on.
You've probably been with this woman for some time now as well. She probably wonders if you'll ever trade her for a younger or more attractive version of her. You're tapping into two major insecurity nodes most married women have.
As long as you amply reassure her, everything should be ok. If she still tries to "ban" porn then calmy explain that you won't. It's one thing to reassure her because you understand where she comes from and something else entire to cater to arbitrary shit like that.
Good luck!