you can't do a thing about it, unless your computer has been specifically changed to disconnect after a certain period... use Internet Connect to see... i'm assuming dialup here...
more than likely, her ISP monitors traffic, and if it does not detect any, it kills the connection after 15 minutes. this is fairly common for dialup. possible solutions: leave an auto-refreshing website up, like nytimes.com (reloads every 5 minutes)... this generates traffic. the ISP may see through this, there are programs out there somewhere to maintain a small amount of network traffic for this very purpose... or you could run a p2p app, something that would generate it's own constant traffic... the question is, if it's dialup, why does she need it to be connected after she leaves?
pnw