If the vaseline is not doing the trick, try extra virgin olive oil. You will find it in the cooking oil section of most health food stores. This stuff is pretty versatile to have around. I use it in my hair, on my body, as a makeup remover (it melts mascara right off your face), and a personal lubricant (ooh la, la)... it also fries up a nice piece of halibit.
Also, consider getting more healthy fats in her diet if she isn't already on some. Or up the dosage of how much she is getting. Healthy fats include flax oil, fish oil, avocado, etc. Not only does it lubricate the skin internally and protect it, healthy fats also help the brain (which is 65% fat) and that can lessen ticks and nervous habits.
If she were my kid, she would be getting a tablespoon of flax oil every day... you can mix it in her yogurt, oatmeal, or put it on toast. You can add it to any food once it has come off its heat source. Smoothies hides it VERY well!
Finally, what ever you do, don't bug her about it...when you have a nervous tick, it is worse when you contiensly think about trying to stop it. Trust me, I know. Just let her be, she'll work her way out of it.