First thing's first: scan the beast, download the information to your log book and learn of its weak spot in its mouth. If you don't do this, killing it will take much longer. Lock on to its mouth and get to work. Stay locked and use the B-button (jump) in conjunction with pressing left or right on the analog to side step. You can avoid the huge green beams of energy that she spits at you. You can also use missiles (Y-button) to speed up the process. The trick is that you have you position yourself so you can shoot through the gaps in the cylindrical blue shield that surrounds her. She shouldn't be too difficult to beat.