Moonkin, sounds like you need lots of reassurance from your T and you are getting some. Even if her daughter gets pregnant, it takes 9 months to grow a baby and a bit of time to uproot oneself and move to another state, so I don't think your T would move to Texas without quite a bit of warning, and it will probably never happen as the daughter is not planning to have kids. It could be that even if this happens, you would not even be around to know of it. You are coming up on a transition in your own life--finishing high school--and may find yourself moving away to go to college, taking a new job, etc., so you may leave your T before she leaves you.
Anyway, for now, it is a very distant possibility that your T will move to Texas soon. Can you put it in the background?
Perhaps at the beginning of each session with your T, you can seek the reassurance that you need that she is not going anywhere. You can hear what you need to hear and then move on with the session and what you are there to work on. Perhaps take 5 minutes with the reassurance and devote the bulk of the session to what you want to work on. Can you talk with her about this?
It sounds like one thing you are wanting to work on is to have more in your life besides just your T. Building up outside friendships and relationships. This is so important. Maybe broach this with your T. What are her ideas? When I began therapy with my first T, one of the first things she had me work on was building up my outside network of friends and family for support. She said to me, "I can't do it all." This was such good advice. If you are very shy and have trouble making friends, this is something you can work on in therapy! Or whatever your situation is... Great thing to explore with T.