NY we already have talked about seeing the same therapist separately, and she was not to warm to it! When we did attend together she felt "ganged" up on. The reason for that was she was down playing the seriousness of the OM drinking and gambling problems, and was not telling the therapist the truth in how she was reacting to him! I would help fill in the blanks, and give the whole truth. This she said was like being ganged up on! She thinks I will be able to influence the therapist to my side and she won't get her views out. AS you can tell my W is a little insecure!
I don't know if it's insecurity on her part, Tim, but that's not so critical here. The point here is that, if you've discussed the viability of both attending the same C and how it would benefit you both, and she doesn't accept that idea, it's telling you something about who you're "working" with. She doesn't really wish to 'work" with you on this. Therefore, this is her problem, all you can do is take care of your problems. If you're dealing with someone unreasonable, it's a waste of effort.
You might try asking her what she then would suggest as a win-win solution. Ask her, "If you were me, what would you suggest that would work for us both?" Try that.
If she then suggests something that wouldn't work for you, ask her to explain how it benefits you.
IOW, you're getting her then to think in terms of being in your shoes, not just hers. If she can't, or stalls or says, "I don't want to talk about it any more"... you know that she's not earnest, and that will tell you something.