Well, if she asks again, you could say that theoretically, a max of about 24 MPix with a 4,000 ppi home scanner (file about 4,000 by 8,000 pix), and about 96 MPix by paying a lab to scan the film with an 8,000 ppi professional scanner (file about 8,000 by 12,000 pix). In practice, I've never scanned anything to make files that large, nor have I ever had a computer capable of working on such monster files regularly.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."