iPhone has addresses - will that first sync remove them?
She shouldn't lose any contacts by syncing with itunes. She might easily end up with duplicates, though, if the same address is in both places. As I understand, every item in the address book is equipped with a UUID. When you delete a record on one device, the UUID is put in a list of deleted records, and so the corresponding record is deleted on other devices during a sync. But that is supposed to be the only way records are deleted from syncing.

Disclaimer: The above is what I have inferred from observation. I haven't seen it in any authoritative documentation, so there is a possibility that it is not entirely accurate. Use this advice at your own risk.