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