find the file name, "A" (refers to the file name, not the file).
put a copy of this file onto a server (windows share or something)
mount a dir on each machine pointing to the share on that server
rename the file on each audrey to not "A" and make a new link from "A" to "B", which is "A" found in the mount point
lets say the file is /a/date.file
copy this file to a shared directory on a server.
make a new mount point, mounting the shared directory. make the mount point /b/ on each audrey.
rename /a/date.file to /a/date.bk on each audrey
link /a/date.file -> /b/date.file on each audrey so that each datebook app points to the same actual file.
this may work. if the apps recognize the changes automatically. It may also horribly fail, but I am pretty sure it won't do harm to try.