In the end she landed ok; she got into UCSD off of the waitlist and is happy there. I do not know how her school handles Val, there could be more than one. I also have no insight into why she was rejected, as we all constantly remind people, there is no way of knowing.
There are a couple of things that do come to mind though. She was applying to challenging engineering majors so that never helps. Her ECs were also strong but she was a VERY stereotypical Asian candidate. The school that she attended as I mentioned was average in terms of SES and a better environment overall than the other student that I mentioned. Looking at the schools success rated for top UCs it isn’t great, generally at or slightly below the overall acceptance rate and they were spectacularly unsuccessful at UC Irvine for some reason and did not have a good year at UCLA.
Overall I would have to say that she was probably in the mix with a few other kids at her school and the PIQs weren’t where the other kids were. I think for her parents the waitlist at Davis and outright denial at UCI were the biggest shocks.
For her non-UC applications she had no success in the T20 and excellent success with considerable merit at the T40/50 level. A typical “average excellent” set of results.