Unfortunately, I’m unaware of any convenient resource where you can find admit rates for CS. Some schools (such as the UCs) publish them, but others don’t. Some schools will probably tell you if you write and ask. Other schools (e.g. Ivys, and most LACs) don’t admit by major, so such a rate doesn’t even exist. So, it’s frustrating.
That said, while it’s true that some top rated schools (e.g. Carnegie Melon, UIUC OOS, University of Washington OOS) have tiny CS admit rates, there are plenty of schools with quality CS programs that have very reasonable admit rates for CS, especially for a student as strong as yours.
Since your student seems likely to be NMSF, it is worth looking into the schools that give big merit for this designation. Here is a thread that describes them. All of these would be admission and financial safeties for your student except for USC (only gives half tuition so might not meet budget, and admission not guaranteed) and Fordham (admission safety, but may not meet budget, and CS not its strength anyway.) Big merit NMF/NMSF schools and their specialties