Well, it sounds like she doesn't have the strength for Power Attack, if she's 15th level and doing 1d4+2 damage. So, there goes the "Hit them really hard" idea.
Without that, and without building the character specifically to be an undead-hating rogue (i.e. multiclassing into cleric and Skullclan Hunter), then the best thing for her to do is go the good team player approach, as outlined above.
Now, if the undead happen to be the kind that explode when they go down, and damaging unattended objects, she may wish to grab any valuable-looking items that drop before they explode. I've done that before when my rogue had nothing else major to contribute, and the priest-paladin was already revved up.
Brad