Per Wiki:
Voyager’s producers reluctantly fired Lien after her personal issues affected her reliability on set. At the time, this was not openly discussed and her departure was attributed to other reasons; these ranged from Lien voluntarily leaving to pursue other roles to her being removed to make room for Jeri Ryan’s introduction as Seven of Nine.
And then she went cray cray.
Indecent exposure to a minor is a slight sign of instability.