Hi Hon,
A thought from a non-transitioning cd. When I'm feminine, I also feel vulnerable. I think its a part of being feminine. (I mean the guy part of me doesn't feel "vulnerable". He may feel "threatened" or "challenged", occasionally "inadequate", but never "vulnerable".)
Oddly enough I cherish that vulnerable feeling. (I remember the first time a masculine person pulled me towards himself with sexual desire -- Ohhh!)
But remember that being being preceived as "vulnerable" does not mean being preceived as "inadequate". And I suspect that what you are describing is a concern of being judged that way because of your voice being feminine. But look at what you have already accomplished! 10 years transitioned? Nobody else in your nursing school will have ever accomplished what you have. So hold your head high (one of the tricks my guy uses) and thrust out your bosom (my guy "squares his shoulders", but its the same thing) and look them straight in the eye when you softly speak. They WILL listen. Your authority comes from what you have made of yourself -- the challenges you have already overcome -- not the lilt of your feminine voice.
Love, Caroline