I too have been caught in a down current, on a reef in St. Lucia where 2 currents were merging, and I (and my OW students) had the bad luck to be caught in the down side instead of the up side.
My DM and certified divers were blown to the surface from safety stop depth. My students and I were doing our dive following the skills portion of OW5 for training and experience, and were at about 30 feet, ready to ascent to 15 feet for our safety stop. Suddenly, there were clouds of bubbles around me (my exhalation bubbles) and since I had the float, my arm was being jerked up. I saw my students plunging to the depths, which was measured in thousands of feet, so I abandoned the reel and went after the students, about 50 feet below me.
I caught the students at some point, grabbed their BC shoulder straps, and motioned for them to inflate. The male did hang on his inflator, the female motioned towards her ear, which was streaming blood, as she had obviously ruptured an eardrum. I could not let go of either diver, the male was providing all the buoyancy for the team, and me and the female were still going down, so I motioned to him to inflate her, which he did. I still didn't realize the extent of the problem, but the down current spit me out at some point, and we all began rocketing to the surface. At this point, I adjusted my own buoyancy, the male had the snap to start venting, the girl was now in extreme pain and unable to do anything, so I let the male go and controlled her and my buoyancy. We stopped at 15 feet for 45 minutes (this was long before I knew any decompression theory) and my computer (a Sherwood ReSource) was flashing 289, as that's all the deeper it reads out.
Meanwhile, my boat crew had called the St. Lucia marine patrol and every dive boat in the vicinity. We were found after running about out of air, we kept enough to inflate on the surface about 2 miles from where we were last seen by our crew.
I only relate this story because I had about 600-1,000 dives at the time, I had no idea what a down current was, nor did I have any idea what to do about it. The 3 of us could easily have died that day. Even though I'm trimix certified now, that is the deepest dive I've ever done. I have no idea of the bottom around Duncan rock, but if it's deep, and Lynne didn't get very positive, she could easily have not taken the steps necessary to get out of a down current. I and my OW students were merely lucky.