Perhaps, but you will still overwrite it when you exit the editor and let sudo copy the contents back (that being said, there might be a race condition between closing the editor and sudo noticing that the process has terminated). Not sure if this would work, but a possible workaround could be to use /dev/shm (https://www.kernel.org/doc/gorman/html/understand/understand...).

The temporary file should be created in such a way that other users cannot modify it. If that does not happen, if other users can modify it, I would regard that as a bug.

Malicious processes running as the same user could potentially modify the file, but if you have malicious processes running as a user with sudo privileges you have probably already lost.

Yes, I think she can. I think this is better than running the whole editor as root.