It's not accurate to add up a registry and interpret that as a total that the couple is specifically requesting. I don't think anybody actually expects that their guests are obligated to give them everything on their registry.
A registry says, "If you need ideas, here are several things that you can be certain I will enjoy."
I *don't* think honeymoon registries are completely polite, but the signals brides are getting from other places are making that sort of registry seem acceptable. And I know many, many guests, esp. younger ones, who think that such a list of suggestions, including " help us with our airfare" or "help us save toward a maternity leave," is a completely sensible gift suggestion.
So I can't condemn a couple w/ such a registry as greedy.
Also, if you want to do something nice, feel free! If you want to find out the color of their china, and then make plate separators from a flannel in a coordinating/matching color, go to town!
If she has the kind of mom you described, I would bet that she would really like it.
Lots of people thoroughly enjoy thoughtful gifts that they never thought of themselves.
Also, I'm the odd person out in that I think gift givers are -entitled- to think of what makes them happy when they give a gift. It's not *only* about the gift recipient.
Gifts are intended to draw you closer. And if you're feeling distance from them with your choice (you feel like you're just helping them indulge in a wasteful way; you feel like you're helping them pay their bills when you wanted a more indulgent feeling attached to your name in their mind; whatever), that's not a good gift.
So if you sort of wanted to give her something pretty for her home that she'd have for a while, do so.