After Sponsor is Approved to sponsor (1st part of application)........PA PR (2nd part of application), the sponsor won't have PA permission to do business on her behalf with IRCC....may not be able to represent PA regarding PA PR application, and may have limited access to information regarding her PR application.
Use of a Representative [IMM 5476] will enable the Sponsor to do business on behalf of the PA regarding the PA PR application.
However, if the Sponsor is Unpaid representative they cannot use online accounts.......only authorized paid representative can link application to their own online account......refer.....
Spousal Sponsorship Guide.....Communicating with IRCC.
Important: Do not attempt to link your application to your personal online account if you have appointed a representative. If you have appointed a representative and attempt to link your application to your own online account, you will have to cancel your representative before you can link.
You may consider linking your application to online account and don't just rely on emails.....emails are not fully guaranteed but messages from IRCC will always be sent to your online account.
You may also consider having the online account (GCKey) linked the application and share the account login info so both Sponsor and PA can login.