Actually Vivian, you shouldn't try to communicate with the psychiatrist beforehand.  Number One, he's only going to take anything you have to say as coming from a caring, concerned, and loving mother (which is significant! don't get me wrong), but what your step-daughter has to say to him is really all he's going to "use" in any decision he makes.  Number Two, your step-daughter is 23, i.e. - an adult, in the eyes of the law (Hippa) and the psychiatrist.  You're right, she has the right to see the doctor without you being present.  I understand that may make you a little uneasy as you want to be there to be sure the psychiatrist knows just whats been going on with her, and, given that she confides in you it may be very likely that she will want you to be there.  But again, the psychiatrist is really only going to consider what your step-daughter has to say.  So, if possible, talk with your step-daughter and let her know just how important it is to you that she be as honest with the psychiatrist as possible.  Help her to understand that her symptoms don't affect her alone - that everyone is affected by them.  As far as meds are concerned, if she's going to see a psychiatrist, it's highly probable that she's going to get a prescription.  If she doesn't want meds, then find a good therapist.  A good therapist may be all that she needs, but from my personal experience, that's not the way it sounds.  With bipolar disorder, meds are usually in there somewhere.  If she's willing to work with a therapist, then it may be possible that she may not have to have a zombifying dose of meds.  In any case, though, I can assure you that a psychiatrist will avoid zombifying a 23 year old as much as possible.

I can tell that you're worried, concerned, and anxious, but that's just because you love your step-daughter.  It's very refreshing to know that there's still love like that in the world.  Again, talk with her and help her to understand that being completely honest with the psychiatrist will help him to best help her and to prescribe the best thing at that moment.  After a couple of months, the psychiatrist may change the medication, but psych meds take a while to work, so she's not only going to have to be honest, but also patient.

I wish you both the best!