Hi, Louisa, and welcome to WriteWords.
Congratluations to your friend on getting an agent, and fingers crossed for the meeting tomorrow. There are far more experienced members here who, hopefully, will be able to answer your question, so I'll leave it for them, but if you need any help navigating the site, then feel free to ask.
- NaomiM
<Added>One thing I will add, regarding meeting the publisher, sometimes there is an offer 'under the table' but the publisher wants to meet the writer first to check them out personally.
There are anecdotes, passed round by the agents, about writers who've blown the meeting because they refused point blank to make any of the changes to their manuscript suggested by the publisher, and are never shown the publishing contract.