Most of the rules and directives ARE meant to be implemented. I understand that UK has the most 'local' rules against them (but are challengeable in court).
I'm sure I've read somewhere that these rules are ALL adopted by Schenghen Area members. Couldn't swear to that though.
I do hope that a simple letter accompanied by a copy of the relevant EU directive will be enough for her to secure her residence.
It should be.
She really shouldn't be forced to engage an immigration lawyer to ensure her rights are maintained.
Just in case, it may strengthen her case to also include reference to the Zambrano ruling.
I wish her good luck.