I raised two boys in Petaluma. 1 went to Casa and the other to PHS. We also hosted and exchange student who attended PHS. Both my sons got good educations. The one that went to PHS actually started as a freshman at Casa and then switched to PHS. The year that my son left Casa to PHS was a record year for transfers (you can read into that what you want). I experienced both schools and I must say that I was impressed with PHS. However the parents who have kids graduate out of Casa that were honor students say they have the best honors classes (and they are very highly rated). My son took honor classes at PHS and they were good as well.
Casa is a much larger school (D2) than PHS (D3) - so Casa is much more diverse and my son experienced racial tension between whites and hispanics (Fights break out every year on Cinco De Mayo). I have parents with tall blonde girls that were students at Casa that got harassed all year - one so much she had to leave the school. Casa's graduation is done in English and Spanish. PHS's graduations are surrounded by American Flags and very traditional.
Both schools have excellent sports programs if your daughter is into sports.
Overall we loved the PHS experience. I think Casa has changed a lot since our oldest son graduated from there.