1. No, you can link it to her GCKey account. You can't link it to both accounts.
2. No.
3. No, the AOR typically only goes to the sponsor (unless you manage to link the application in the few hours before it being linkable and the AOR being emailed, in which case it will go to the email address of the GCKey you linked the application to.
4. Because only the sponsor is sent AOR - which is the correspondance.
As for the lack of success in linking, you may need to call IRCC. Sometimes multiple surnames (such as Spanish/Latin style surnames) get truncated/combined/something funny happens, though using application number and UCI should have eliminated that issue.