Are the original video files stored in your computer, in your Google account, or both?
I am not convinced that the file sizes are the issue.
FYI (from Google Support):
https://support.google.com/a/users/answer/7338880?hl=en#:~:text=a shared drive.-,Upload & copy limits in shared drives,to 5 TB in size.
And it is not that you or her that is doing "something wrong" per se.
The premise has been that you are trying to share large files with her when the requirement is that you upload or otherwise need to place copies of the videos into the target Google Drive that she has created.
So when you share, the file is in your account and taking your space.
Think in terms of "upload".
https://www.wikihow.com/Share-Large-Files-on-Google-Drive
(Note Part 2, #1.)
Specifically:
"Understand how files are shared on Google Drive. There are essentially two different ways that you can share a file that you've uploaded to your Drive: you can share it with specific Drive users, or you can generate a link that anyone can use to access the file."
My thought is that the process has gotten just a bit mixed up.