I'm having a hard time Googling to find advice for this particular situation.

Person A and Person B are in an intimate relationship.
Person A is in therapy.
Person A receives an email from Person B.
Person A would like to discuss the email with Person A's therapist.
Is it OK for Person A to forward the email to Person A's therapist without prior permission form Person B?

I can find links that address in general forwarding another person's email without their permission.
I am trying to find an answer that is specific to the therapy situation.

Any info or thoughts would be appreciated.
Any reference to some kind of "best practice" or "industry standard" answer would help a lot.