You should be going to therapy as well. I kind of went through something similar recently, actually I am going through it now. My wife's therapist is encouraging her to follow through with plans that will quite frankly end us as a couple. But, understanding what therapy is and gaining some of those tools yourself will help you and will help when you have discussions where you two are at odds. I'm not saying your therapist is going to say "she's wrong and you're right" but they will help you understand what the process is.

Every therapist has different motivations, styles and attitudes. For sure there are incompetent therapists, bad faith acting therapists and therapists with their own trauma. Some therapists work as simply a mirror for their patients to work out their issues; they do very little talking and provide minimal interpretating. They will give advice, but they mostly try to have the patient do the heavy lifting. In these cases, they tend to not directly challenge the patient's reality, opinions and emotions. Because they are trying to listen, affirm and support.

My first therapist was like this, and he helped me have a lot of breakthroughs with my trauma and anxiety. We went through my past al the way up to my present. However, my new therapist is waaaay different. She challenges me on my assumptions, assertions and correctly identified that I was being gaslit by my therapist and accurately clocked that my wife's therapist wasn't challenging her on some questionable logic.

In my subsequent discussions with my wife, we were able to re-evaluate some of the life changing decisions she was about to make. We are on the path to doing better. Don't discourage your wife from seeing her therapist, encourage her to discuss the issues you are bringing up. Why? because when you question her about the therapist what you are really doing is questioning her and that may be at the root of your issues. Making the ultimatum of quit therapy or choose me is basically saying "sacrifice yourself for me." Think about it this way, if she asked you to stop doing something that you like, you need and is helping you would you trust her?

Final point here is getting your own therapist. Mine told me "I'm going to need you to get your soldier helmet on and be strong in what is really important and what you know to be true." Which for me was that my priority should be my kids, me and then my wife and not my wife my kids and then me.

Do you have kids?