I would suggest setting up a private share for `andrea' and try logging in. Make sure that authentication works for user `andrea'. If it doesn't, look in the logs for info on what the problem is.
Did you try adding `andrea' to the read list of your public share? Add it before the @users group.
List the permissions of the /data/Music directory: ls -ld /data/Music
Is Andrea the owner? If not change the ownership of the directory or use setfacl to give andrea write permissions
setfacl -m g:u:andrea:rwx /data/Music
setfacl -m u:andrea:rwx /data/Music
I'll guess that the owner is "andrea" and the group "users" with rwx-rxr-x permissions set.
As you probably are aware, the 'guest' user in windows is equivalent to the 'nobody' user in Linux. The 'o' permission bit for r & x needs to be set on the directory to allow nobody to read it.