I watched the video on YT at 0.25 speed, it's pretty clear to see what happened (I see three instances of contact):
At about 44.2 seconds on the race clock, Mu runs up a little too close to Moraa and runs into Moraa's right arm which causes a slight hitch in Mu's stride.
At about 53.7 seconds on the race clock, Mu's left leg is full extended behind her and as her foot is cycling through it contacts Sekgodiso's right knee, right on the knee cap. Sekgodiso had just thrown in a mini burst of speed to tighten up the gap so she's closer than Mu expected. You can barely see Mu's stride hitch (looks like she leans back a little and her hands come up a tiny bit).
At 1:08.0 Mu is crossing over the lane line from lane 2 to outside of lane 1, right into Sekgodiso's space. Any normal person could probably have pulled it off but Mu has such a gigantic stride there was no way she was fitting in that space. Sekgodiso's right quad contacts Mu's left leg just above the ankle, sending Mu's left foot into the back of her right calf, hooking it, which causes Mu to stand upright, the left foot to reach farther into lane 1 searching for balance, and then it cycles back straight into Sekgodiso's right knee, causing her to fall and propelling Mu out towards lane 2.
Mu seems to have a very upright stance, and her upper body is almost leaned back, which weirdly caused her to almost fall backwards, which is why her body motion is kind of unusual (I would have expected her to be pitched forward and trying not to fall on her face). When I saw the race in real time, I thought she was putting the brakes on and going to quit, but after watching it in slo mo many times, you can tell she is fighting as hard as she can to stay in it.
It's unfortunate that the greatest talent ever in the 800m is someone with such an incredibly big stride that she'll struggle to run in a pack without problems. I don't think this was a DQ worthy offense on Mu but Sekgodiso should be put in the final.