Make sure that you have your Force Shield up to level 1 or 2 before the battle with Maris begins (depending on the difficulty). When Maris becomes invisible, charge up your Force Shield. If it is at level 2, the arcs of lightning will show where she is. You can attack her while the electricity has her stunned. If it is not at level 2, try to randomly attack when she is invisible or use the Force Shield while she is still visible to get easy hits on her.