Is finishing high school really such a big deal over there? I would have a family dinner and buy her a present that will be useful in college.
Yes and IMO it is WAY over the top. At some schools 8th grade promotion is even a huge deal.
My kids attend is fairly typical for a US High School. Formal portraits are taken the summer BEFORE H.S. graduation. Including formal pictures in a cap & gown if you want. Seems a bit presumptuous since although MOST do graduate it's not a done deal. Stuff starts to come in the mail soon after. When my daughter graduated we were mailed a catalog with everything from class rings, t-shirts, sweatshirts, necklaces, and fancy formal graduation invitations & announcements. Imagine the money someone is making on some of this stuff.
About a month before graduation is Senior Prom which is a formal dance, formal ball gowns, tux's, shoes & accessories to match, dinner before, limo's. Some teens & parents go all out. These days Prom is really more a H.S. right of passage than a graduation events.
There is a yearbook that is put together by students. Yearbook is one tradition I like, and I still enjoy my yearbooks. Yearbook is a year long class where students learn page layout, photography, graphic design. There is a huge graduation ceremony put on by the school district, senior "skip" day, a class field trip (often do Disneyland since we live local). And to top it off "Grad Night" party that goes all night after graduation. Note: one upon a time Senior Prom was the graduation "party" but that has evolved and these days that now happens a month or so earlier. Most of these events COST $$. Everyone received 4 free graduation tickets, more cost extra. Our PTA has some money set aside every year to enable a few kids that can't afford it to go to some events.
The "Grad Night" party is something H.S. PTA's started sponsoring 30+ years ago to keep kids a SAFE SOBER place to party with their friends after graduation. Too many kids were going out drinking & driving, and killing themselves on their graduation "night". The party my daughter attended was NOT formal, the kids were bussed to the location and the kids played games until 4AM.