Well your in luck sort of. I suggest you replace the door (damage around the door handle can be tricky for someone new to body repair) and bump the rear quarter out. Since it is the vent side you can remove the cover over the vent and remove the rubber thing and get down in there to try and push it out again as best you can then work from there. You will need to get the frame where the door attaches as original as possible so you minimize the gap and amount of body filler needed. What you can't push out through the vent use a screw in slide hammer to do. If you still think it is beyond body filler after that then think about a rear quarter, it is strange sounding but you need to get the panel as undamaged as possible before you replace it so it lines back up easier so even if you are set on replacing the rear quarter push the old one into place first then cut and weld. Doesn't look unrepairable though and white is easy to match and covers imperfections well.