Excel open in app via share link

Hi! I shared an Excel document with my boss. We work in it together. I can open it in the app. But she can't. She can only click on the button 'open link'. I open the file via my One Drive, but it is not in her One Drive. (yes, it is the same e-mail)

Also when she opens the file in browser, she doesn't get the option 'open in app'.  She would really like to work in it in the app. Because in the browser version there are missing options. Any suggestions?