I am not from the US, but no doubt some of your fellow Americans will be along in a bit. I congratulate your daughter. Corpus is a lovely college and PPE is an interesting degree. I hope that your daughter thrives academically, and has a wonderful time socially.
I studied Modern History at Wadham many years ago, and had a great time. My daughter starts at St Peter's in October, reading Jurisprudence. Perhaps our daughters will meet one another.
PS: If you have not already done so, maybe have a look at the Oxford Parents' Association thread - it contains much useful information about the Oxford experience.