Is iChat a chat service? I thought it was just a program that connected to a bunch of different chat services, like Trillian or Pidgin.
Edit: also, I wouldn't necessarily be too concerned about the message you send by signing your daughter up for a full-blown AIM account. Respect for idiotic corporate bureaucracy isn't that important a value to impart, is it?
Another edit: doing a little more reading, it sounds like her friends are probably using iChat to connect to AIM, not the other way around. If so, there's no way around the need for an AIM account, unless your daughter can be a hero and convince all of her friends to use Gtalk.