If you really think there is an issue, maybe ask the high school counselor for some feedback on the strength of her COSMOS application and her strength as a UC applicant. Maybe there is something she is missing or some aspect of her application (essay, etc) that was not quite up to par.
Also, UC essays do count for a lot, so definitely put time and effort into those. Too large a list of schools with lots of supplements can be really demanding, start writing drafts now for common ap, UC essays, any prompts that are published, etc. The essays can be rewritten and repurposed, but they definitely get better in each iteration.
And use FIRST to your advantage, there should be someone who knows how to use FIRST participation to get a bit of push into a STEM program.
I am thinking that open houses and likely summer programs are geared to underprivileged students, including many races and backgrounds, rural and urban, and likely not from top CA schools. Sometimes, you have to admit your kids have a lot going for them and others do not, and as you say, she had lots of other opportunities.
A FIRST participant probably wasn’t an ideal audience for a “look what STEM can do for you” type program. I think a lot of these programs really are trying to find talented but outsider students who can grow into a UC STEM program.