Maybe diving without you. It's worked for me with people with anxiety issues. I've experienced one person of a couple or group/family that has had issues that needed to be given confidence and empowerment to dive without the person/family members, showing them to be totally independant and encouraging them to take "possession" of thier own dives instead of feeling pressure or guided. (even if you aren't) If she really wants to dive for herself she will!
I was going to add something along these lines. My partner is a rather anxious person. When I got a chance to sign up for a certification class in May, I did so with a friend. I signed her up for a 2hr intro class in March. My theory was if she liked it then awesome she'd still have time to get in on ours, if she didn't I already have a buddy.
While waiting for this class I made only plans for myself and my buddy, I'd say when he and I do this or when he and I go to X location you can sit at the beach and we'll be back to meet you. Thing is I wanted HER to choose to or not to do this. I typically drag her along on land adventures and after she loved them. However diving is a life/death thing. I don't want to drag her on this one.
So last weekend she took the intro class and liked it. She's been snorkeling with me a zillion times so she was ahead of her class. Upon leaving the class she'd signed up for the class my friend and I are in.
Here's the IMPORTANT part. She wants to not have me as her buddy in class. At first that might sound odd. However it's perfect really. She has a chance to not rely on me, I have the opportunity to not take care of her. She can go and work out her issues and not feel any pressure of being watched, judged, failing to meet goals for things like trips and vacations. She will be her own person and gain the skills herself. I think sometimes we forget after being with someone a long time how much we look out for them. She might need to build her confidence with diving on her own a little.
Personally I'd tell her to sign up maybe for private lessons or with another group of women. Women tend to "get" each other and know how it is to have anxiety, wanting to please their partners, ect. Let me her this her own. Own pace, own trials, and own rewards. Hopefully she'll come out as a GREAT dive buddy who's confident and you'll be very happy for it.