I was gonna say “your wife is always right even when she’s wrong” because that’s my basic advice, but using pornography as a topic for a 4th grader (she’s my oldest son’s age) would be a bit too much. It’s not that kids should grow in a bubble or anything, but it is a topic that opens a six-pack of worms an with kids that age you already have enough.
The topic seems to have originated with your wife.
Stick to your guns.
Maybe you could steer the topic towards giving women all the chances they need so that they don’t feel presured to do porn?