Your very perspective, and a good friend. It's difficult for somebody to see in between theirs eyes without a mirror. The only way she will be able to see her behavior and how she allows her self to be a stool is if somebody she trusts and cares about shows her through the mirror. You can see her behavior better then she can, so show her.

Then after you make your friend aware of what you see make some suggestions that could boost her role in the her marriage. Like for example, encourage her to speak up and to have an important role. It may even help her husband understand her feelings as well.

I hope it all works out for your friend.