anyways i have the witch from chapter 5 to enter the tower and im in with no idea how to find the moth girl
sure, the mothgirl is the first sidequest opened when you get in the tower of wisdom. the first time you get in you need to talk with Council Advisor Galatea with Enilynn in your party (the green hair illussionist).
Galatea will give you the chance to re-join the school and open a set of random sidequests, but first you must complete a first sidequest job, which is defeating the Mothgirl, which roams in the Forest of Lys (upon you get the sidequest, the mothtirl will spawn eventually in the south-east area).
I hope this helps to meet the moth girl ^^