From both Susie and me, our best for a complete, if clearly not speedy recovery.
My wife and I both commuted by bike in Seattle for most of 35 years. I logged 50k of urban commuting miles. Hers was shorter.
Twice I have gotten calls from the emergency room. The first time, she said through sobs, "I'm all right!" That was not a very convincing statement. She had been taken to University Hospital with a broken collar bone. Susie has a huge tolerance for pain but nearly blacked out as the teaching docs manipulated the break a few too many times. She was not struck in that accident but had crash over a curb to escape an old guy in a pickup truck who turned left in front of her. He thought she would turn right onto the freeway. Go figure.
The second emergency room call was from a hospital staffer telling me where she was and added reassuringly(?) that Susie was conscious. She did have a concussion, but recovered rapidly. This time, she was struck by a left-turner at an intersection. The driver was upset on several levels, being a regular bike commuter herself. She was late for work and did not see my wife crossing from the other side of the intersection.
After that, I told Susie I was simply not going to accept any more calls from the emergency room!
I do my best to track what's approaching from behind through the use of my helmet-mounted rear view mirror. In busy traffic situations, most of my attention necessarily goes to what is in front of me. If I had been in your wife's situation, Tom, I doubt I would have seen it coming. A car's swerve or drift due to inattention happens way too fast.
I often joke that my brand of defensive riding is that (1) I am invisible, and (2) that every car on the road is trying to kill me. That attitude has saved me from accidents a few times.
The hazards from behind, I'm a bit fatalistic about. On our cross-country bike trip, day 2 took us over Snoqualmie Pass on the shoulder of I-90. The shoulder was very wide and the biggest hazards were road debris. Then I heard a banging and clattering behind me. I saw in the mirror an RV lumbering up the grade behind us with its right hand boarding steps extended. The rig cleared us by at least 15 feet. Fortunately we were not on a two lane highway with no shoulder at the time.