M.Z.
My 5-year-old son does this-- my 3-year-old daughter does not--LOL. I have read that it is due to stress from the day and they do have stress. What I have noticed is that my son is a very anxious kid to begin with-- he is always asking lots of questions and has to know everything about where we are going and what is going to happen-- not ridiculous but he is much more aware of the world than my daughter. My daughter is care-free and lives on the edge. So, I guess my point is that it is connected to their personality as well-- I have been told they will outgrow it eventually and my kids started to see a pediatric dentist since at 18 months-- there is nothing we can do for it. If you really are concerned-- take her to the dentist for a check-up and discuss it with them. Best of luck
Mel