I don't use Itunes much, although I know it can have problems importing playlists and sometimes does things to your music you don't want.
That being said, we need to be clear about one thing: a bunch of music files is just a bunch of music files; it's not a playlist.
If you give her a bunch of music files in m4a format, you haven't given her a playlist. You've given her a bunch of files. The individual files do not know they were on a playlist, nor their order.
If you want to share a playlist, share the actual playlist FILE. It contains the names of the files in the playlist, IN ORDER. Without the playlist file, it's just a bunch of files, not a playlist.
To make it simple for her, create the m4a files on your computer, then put them all in the same folder. Now add the M4A files to a new playlist, in the proper order. Your original playlist file has the flacs, not the m4a files.
Then in MC do File->Export Playlist and select a "M3U Playlist (simple)" as the export format. Make sure the option "Store paths relative to the playlist location" is checked. That M3U file is the actual playlist. Make sure you save the playlist to the same folder you have the M4A files in.
This is a pain because the playlist specifies the path to the file, including the drive letter and folders, and it won't work on the destination machine unless the drive and folders match. And drives never match between PCs and Macs.
If you've done it correctly, if you look at the m3u file with a text editor, all the lines should start with .\
Give her that M3U file, and the audio files, and Itunes should be able to import it.