The application is done on line so when the account is set up both you and her can upload the required supporting documents to the application. When I did one for my wife I created one "invitation" letter and addressed all of the requirements from the application website with references to the uploaded document(s) which related to each as proof that the requirement was met/covered. Check your inbox.
Your airline is where proof of onward travel is more likely to be requested for people arriving on tourism entry stamps (currently 60 days) so it's best to ask them what their policy is.
If there is a home visit planned during the under-consideration then an exit/re-entry can be done by co-ordinating with the Immigration Office at the time of the extension application