It may be just the opposite. Your T may have walked you in/out initially as a formality-- so that you knew the way, so that you would be more comfortable, etc. Now that you're not "new" anymore, you know where you're going, and you've become more comfortable with each another, she may not think it's necessary. So, perhaps, the fact that she isn't walking you in/out is actually a sign of closeness.

In my own experience, when I began therapy, T used to stand up and walk me to the door at the end of sessions (about 5 feet). Over time, she stopped doing that. The way I take it is that she trusts me to make it those 5 feet on my own. (I have similar confidence in my abilities, so it doesn't bother me in the least ).

If T no longer walking you in/out is bothering you though, you should bring it up with her. I'm sure she has no idea that it's caused you to question your relationship with her.