there is no counseling that will help if your partner is not interested...
the comments are right...my wife and my mom hated my therapist... my mom called her a "guru"... just telling me what I wanted to hear.....heh...she was kind of right in a way!!

in my opinion
here is what can possibly help...

you gently tell her what you are doing...AND YOU DO IT....
its not a question...its not a negotiation.
she can say anything, do anything, threaten, cry, etc... not going to change anything...

and what do you tell her you are doing??
all you are doing is going to a therapist and considering measures to mitigate your gender dysphoria...
you've repressed it for her...and its killing you...its killing you... you are in despair...
and you've come to the conclusion that the best way to get out of despair is to explore your gender fully and openly...and you've already given a lot of thought and in your mind you are trans and that is what you want to talk to a therapist about..

that statement is crystal clear...and its perfectly true... anything more just complicates things..

and you cannot make any promises about what that means or doesnt mean...its a search...you are finally going to help yourself get better....whatever that takes, whatever that means...
talking about things in the future like transition makes no sense if you haven't even gone outside as yourself yet...

I cant lie...we've talked a lot...its very unlikely to go well... and I doubt it matters much what you say or how you say it...so its important that what you say feels RIGHT TO YOU...and works for you...
because that is what you will be left with... and you dont want the doubt of "did I say enough? too much??"..etc.. you cannot be in a position where you've made comments or promises that will make this therapy harder or any progress slower...

there is sadness and loss involved...she has controlled your situation and now you are taking control... that's what will need to be understood...

I urge you to not think too much... to keep it simple and to not back down if you are challenged...

also..you might hate this...talk to a lawyer...you have rights... my ex kicked me out... I left ...I never should have done that..in the end it worked out as best it could, but if this becomes a battle you will need to be prepared to not make mistakes that will cost you a lot of money or lose property... she cant kick you out ...you kick her out..lol..see what im saying??

I feel bad for you guys because I have been through it, and ive seen it..... but on other hand, life moves on and on the other side is all the stuff you want to start working on to live your own best life..