I would not put anything oily next to the delicate eye tissue - especially vaseline which is a petroleum jelly!
The problem is not her eyelashes. The problem is that she has some kind of anxiety (constant or fleeting, doesn't matter) and her choice of coping mechanisms was a form of self-harm or self-mutilation, however tame it might be. I think your absolutely priority should be to identify the issue that prompted this, and figure out why she chose to take it out on her body.
Have there been other occasions like this? Is she part of a social group or does she have even just one friend who engages in this sort of thing (could be cutting, could be anything)? Where did she learn this or what made her think of it?
Talk to her doctor about finding her perhaps a counselor or even a life coach to help her focus on her goals, unload the stress, and establish other strategies for managing her pain and worry. It probably isn't going to be you. I say that because most teens don't turn to their parents anyway, and besides, your instant reaction was to find a home remedy for the eyelashes rather than get to the root cause of this. The cosmetic part is not the most important thing! It's not what she did so much as why she did it. Just being "nervous" doesn't prompt most people to harm themselves. I think an objective professional who can spend maybe a short amount of time (a few sessions, unless it's a deep-seated problem) would be your best bet.
I would also let her school nurse know, in case there are other kids doing this, and so the teachers can be on the alert for other signs of nervousness that are prompting her to do negative things.