What we do that helps is at the beginning of the session, or after the 5 or so minutes of catching up about daily life stuff, is close our eyes and she does a meditation aloud for me. She reminds all parts of me (particularly the child and protector parts) that they are welcome, it's safe to share, and that she loves and cares about them.

I think that the song idea also is great! I might try that one myself as well - a song that signals to my mind that it's time to do therapy... not sure which one that would be?