I'm sorry your dog is sick. It's so difficult to see them hurting. is also difficult to think of life without them...
I think being honest with t is probably a wiser choice, though I know that too can be hard. Maybe t can help you through some of this anxiety (coz right now, without knowing what's going on with your dog, it's just anxiety about her passing, not a definite). I know it's scary, but your dog is still there with you right now. Try to be in the moment with that and enjoy her company... reach out to t, let her know what going on, then spend some quality time with the pup.