The first thing coming to my mind is that your PT is a medical professional and she hopefully could take honesty in a professional way. With growing breasts comes some pain and the PT needs to adjust a little bit.
I was in a similar situation a few weeks ago - I have been seeing a chiropractor and massage therapist on a regular basis. And it just was too obvious due to nail polish and a lot of other changes. Interesting enough, it was the front desk girl who figured it out and directly asked my wife... technically not really OK of her but in the end it helped both of us and my wife agreed that it is time for the big coming out afterwards.
Since your PT also knows your wife, you should talk to her first and make sure she is on board with you telling. Much better than a bad surprise if she gets asked.
The alternative is that you could just blame it on other medical issues or medications you are taking.
In general with doctors I do not hide it. Latest if they see the list of medications I take, they know. Spiro is something cis men take too, but in combination with Estrogen and Progesterone?
Good luck and keep us updated what happens!
