Sam,
Pass on some important advice to your friend's daughter. I don't know what her age is, but if she is at least a teenager on up, please make sure she is with someone who knows the island very well, no exceptions!!! I love my people, but there are some locals that will take advantage of mainlanders. Also, the locals are referred to as either Guamanians or Chamorros.
Here are a couple of nice to know phrases to pass on to your friend's daughter:
Hafa Adai (Hoffa-day) = Hello, how are you
Todo Mauleg (taw-doo-mall-egg) = I'm doing fine
Si Yuus Maase (See-zoo-oos-ma-see) = Thank You
That will make breaking the ice a lot easier.
Darrell