I think I agree with Tracy, below. But I would also throw this out there, since we're all just giving our thoughts...
Has it occurred to either of them, that the longer they put off actually doing this, the more weight he is going to feel to have a bigger and better ring? I know plenty of couples that have been married 20 years, and even though they are quite well off now, they have tiny little rings, because that's all they could afford way back when. The more established the finances become through the years, the more pressure he is going to feel to provide her with a ring be-fitting her "status". Young couples often can't afford an extravagant ring, and nobody ever gives it a second thought. At this point, he has got to feel cornered... he has put off the "proposal" so he can get her a nice ring for how long now? And how close is he to being able to afford what he now feel he "owes" her for waiting? Do you see what I'm saying?
For what it is worth, my own mother doesn't even HAVE an engagement ring. They didn't have a lot of money, my dad was in the service, neither family had heirloom rings to pass down.... My mom wears a simple gold wedding band, and so does my dad. That's it. And she has never taken hers off of her finger even once. Now that it has been almost 50 years, he has of course, during the course of their marriage, given her anniversary rings with lots of diamonds. But none of the diamonds matter like that little gold band.
If your friend would feel like that, then maybe she could suggest to her wanna be fiance, that they should skip the engagement RING, just have bands, and then he can give her a nice anniversary ring later (maybe even a ring celebrating how many years they have actually been together, not just the married years?). Then they could get married, but avoid the whole engagement ring debate.
Just an idea.