Spoiler Alert!!

Like many people, I was doing The Waters of Life quest where your father just died and you're in the tunnel. Dr Li is supposed to stop you and tell you Garza has a heart condition but she got stuck and wouldn't proceed. I tried dozens of things. It took like 3 hours but I finally found something that worked. I should point out, when I was doing this quest I exited the tunnels at the citadel and instead of attempting to complete the quest I ran off and did a different quest. When I went back I discovered the problem with Dr Li. I tried killing everyone and dragging bodies to different points. I tried resurrecting the ghouls and let them kill everyone. I tried to back track all the way back to the project purity control room and resurrected everyone in there. Imagine talking to your dad after he already died, lol. Apparently that approach has worked for some people. Back track to where the energy barrier is, open the command console by pressing ~ type "tcl" and hit enter...without the quotations though. That turns off collisions. Go through the energy barrier and turn on collisions by repeating the previous step. Then go back to the Jefferson memorial and zone back in to the tunnels, and sometimes for some people Dr. Li will reset back to that point. Well that didn't work for me, but I did do that in this instance but when I walked back through the energy barrier on my way to the citadel I didn't turn off collisions and I floated up, in the same room with the energy barrier, past a fence where originally there were a couple enclave soldiers firing at you from up above. I went up there, enabled collisions, looted the corpses then went over to a ladder that went nowhere. But I attempted to go up it a few times and then turned around and left through a door at the end of the platform. Keep in mind, you can't get up here under normal circumstances. You have to float up by disabling collisions. In that room you can jump down over the railing to an area where you can normally access between where Dr Li and Garza get stuck and the citadel exit. Then I back tracked to where Dr Li was stuck with Garza. Garza was there but Dr Li was not. She reset back to where she should have been and I talked to her and was able to complete the quest. I hope this helps somebody. It drove me nuts. You can't use power armor unless you complete that quest and I have a huge stockpile of all different types I was eager to use.
The main "fix" for this problem is supposed to be, save often. Pfft! My last save before that point for me was 22 hours back. No way in hell was I going to repeat 22 hours worth of questing just so I could use power armor and complete the main quest. Don't bother searching for other solutions, I looked at all of them and anything relevant is contained in this post.