Transitioning from MS Outlook on a PC to Apple tools on a Mac

1. Yes a thumb drive or an external drive formatted as Fat or eXFat will work. If its formatted as NTFS for Windows, macOS can read it, but cannot write to it.
2. She can just setup the account in the Mail App on the Mac and her mail should appear immediately.
3. Same thing as point number 2. Adding the email account will let you bring in any other associated data including Calendar, Notes, Contacts etc...

See here: link-> Add email accounts in Mail on Mac - Apple Support

If it's an actual Exchange account, or Hotmail / Outlook.com account you can add it using the Exchange preset.

If she would prefer something that looks and behaves almost the same as Outlook, there's the free eM Client.

You can use the basic instructions I wrote here to get the contacts from Outlook to eM Client. For files and folders, create a folder on the desktop for each local folder she has in Outlook. Drag and drop the emails from Outlook into each same named folder. All attachments will automatically be included. Copy the folders of saved emails onto a flash drive.

Go to eM Client and create same named new local folders. Drag and drop the files from each folder onto the flash drive into eM Client.

I had originally exported the data from Outlook for Mac and them imported it eM Client. Yes, it recreates all of the local folders and brings in the emails, but all with the time and date of import. Doing it the manual way above preserves the original timestamps of your emails.

No idea how to get the calendar history over. Possibly part of an Outlook export?