That would kill me. I see my T in her home and she always leads me or follows me to her front door and says goodbye or "See you in x weeks" or whatever. It's so important to me. If I was in your situation I would be really nervous about mentioning it to her, especially when you hinted about being observant already. Maybe her mind is just very focused on her next client? Like she is headed to her desk to read her notes or whatever?

I feel as if you shouldn't have to say something twice with a T. Especially something so simple that she could easily fix. If you feel able you could say outright, "I would really appreciate if you called goodbye to me at the end of our sessions" or do it yourself - and she could follow your lead. Otherwise I think just leaving abruptly to see if she notices is a fair plan too.