I agree no set rule as long as both are happy.
I think if people are married or living together, and one is a much higher earner than the other, but doesn't share, they simply treat the other person as and when they chose, but they maintain control of "their" money, and the other lives "poorer" and has to show gratitude and wait for hand outs in the way of gifts, then there is inequality there.
The ops friends may be in a different boat, if this guy isn't a high earner, and is buying her thousands of pounds worth of gifts, then it could be he has a significant debt problem, or she does, she's buying it for herself and saying it's a gift from him, because she knows the op would immediately know there is a debt problem if she did say she wasn't buying it.
Sometimes people want to portray their lives in the most positive light, and trying to make thr op feel bad about her husband not buying her expensive gifts would indicate to me this woman has a hidden story and is trying to make herself feeling better by making the op feel bad.
It's look at me, my husband spends thousands on me, yours doesn't on you, poor you, don't you wish you were me?
When in reality it's either "my husband doesn't share money, I'm skint, and I have to wait for him to decide to buy me something, I don't get to decide" or " I've got significant debt and I don't want you to know that, I feel shit and want to make you feel shit because I'm jealous you earn more and don't have debt problems".