I recently had that opportunity too, but I did not do it. But that's partly because I have a history of being a dedicated boundary buster in therapy and I've just recently broken that pattern, so for me, having a mutual friend would be "too close" to that old pattern and I did not want to put myself in that kind of tempting situation. I knew my T wouldn't think it was good for me, either, so I chose not to. But that might not be the case for you and your T. Maybe talk to her about it first and see what she thinks before you decide.