I have a close family member with it, got very serious before he was dignosed and he was very seriously ill with it. I guess it depends on severity, whether it is primary or secondary etc... I'm sure Sqad will be much more informed.
I'd say a health warning bracelet is a must so that if she is ever in an accident or anything like that it is clear to any health professionals so that they can treat accordingly.
Being able to recognise signs of a crisis as early as possible too and have a back up to help eg emergency injection (I think) and people around her who know what to look for and what to do - I guess like for people who have conditions like diabetes/epilepsy.
Again, these kind of things may be OTT as I'm generalising and on the more severe side and don't want to seem over dramatic!
You could find some support groups she could join? Get more advice and support from them?
There is a group here:
http://www.addisons.org.uk/