* Strongly recommend you pay close attention to Nick Dokos--he's brilliant--agree totally with his suggestions; "hardlinks cannot span filesystems" etc.
** "hardlinks breaking"--in rsync I throw -H to include/follow hard links across filesystems when syncing.
*** I'm with Nick though again--not sure what you mean by "hardlinks breaking"
* Thanks for the "syncthing" link and comments--its open source:
Syncthing replaces proprietary sync and cloud services with something open, trustworthy and decentralized. Your data is your data alone and you deserve to ..."
** Sounds great, hope its easy to implement, thanks.
*** I prefer rsync for such problems at the moment.
* Suggest you use FuseFS and sshfs---and on her MacOS she can use BREW to install the FUSE .DMG package and use OSX shell to get to the filesystems that you're willing to share (you mentioned you were worried about providing too much).
** Not recommending SAMBA+CIFS protocol--especially right now, since there is a vulnerability to be revealed on 12APR16
** Or you alone could use FuseFS and sshfs the dirs you want her to have access to on the machine you both share/access (you seem to indicate she has full and comfortable access to those dirs already--so installing the FUSE .DMG package is probably overkill).