Hello Shelley
I know exactly how you feel. My wife started seeing a therapist a while ago and I was worried as you are, that the therapist would advise her to leave me, even though we had/have a wonderful relationship. I too felt that I wasn't in control, but then I realised that could never be in control of her, she does have a mind of her own, so I stopped worrying about it. My wife still goes to therapy but not as often and she is even thinking of stopping all together. One thing to remember is that your wife needs someone other than you to talk to about this. Without risking embarrassment, she can't really discuss this with her friends, or even family members so a therapist is a logical choice.
Just remember Shell that you can't do anything about her wanting to see a therapist, just try and be positive, and support her in her decision. I know you fear that through her therapy she may decide to move on and start a new life, and it is an eventuality you may have to face, just be sure that you have plans of some kind should this happen.
I know that staying with your wife is your goal, and we've chatted about this before, just remember that in order to do that you will probably have to make sacrifices, and compromises in order for this to happen. I would also seek therapy Shelley, it can't hurt and it would show your wife that you are being pro-active as well, who knows maybe between the therapy you may find common ground you can live with.
Keep us posted, and take care.
Steph