Thx. My wife's doing exactly the same thing (it's how we met). But she's only lost a fraction of her goal weight and it's bumming her out. I tell her it is simply the metabolism: Guys just burn calories way faster. I'm 6'4, she's 5'9, and I just burn it a lot quicker.
It's starting to bug her, though, to the point she doesn't like to go out with me in public anymore. (When we were both heavy it wasn't a problem.) And that doesn't help because the temptation is to simply give up and stuff her face full of popcorn in front of the flat-panel. I just tell her I love her and don't care how long it takes, just do your best. She just needs to be patient and she'll catch up eventually. Her health is what matters.
She’s lucky to have you! :) Keep approaching it from a health issue, if that helps. Make sure she knows you want her around to love for a very long time!
(See if she’ll look into a consult on depression; that’s an underlying issue on so many addictions, including food addictions. Bring that one up VERY carefully. You know her best.)