Hello Milkwrapper and welcome
What she'll need more than anything else is that friend that was there before she went into Renfrew.
You don't want to treat her with "kid gloves" or she'll sense somethings different.
Trust me,she's learned a lot about triggers,foods to avoid,when to say no or know that enough is enough.
What you're getting is a better educated friend who now knows more about her eating disorder than she ever did before.
Be proud for her(I don't know why but I envision heartfelt tears) as she now has to acclimate to the same familiar surroundings.
Realize also that there's a plethora of information on this site for you to view at your convenience.Many helpful threads and posts to help you feel more at ease with it all.
I hope this helps;truly