My sister invited me to her Google Wifi network thru Google Home as a manager so I could help her.
Google Home however does not present the Wifi icon so I can do wifi activities (like Mesh tests) on her network.
I can however see and manage all the Homes I have installed myself.
Can an invited Manager see and manage Wifi access points?
Yes, you should be able to unless something changed recently.
Can your sister see Nest Wifi in her Google Home app? For some they disappear from the app, where force stop and clear cache of Google Home sometimes helps. Factory reset and set up from scratch in worst case.
Could also be that you've taken steps to secure your Google account, which included disabling integrations to 3rd parties. Which could cust Nest out of your Google account.