Rescue Remedy is a GREAT way to go! It's safe for cats, dogs, any kind of animals, really, humans, ANYTHING! Even plants, oddly enough.
I take that when I'm stressed.

They also make unique ones, like ones specially designed for anxiety, or panic attacks, or sleepiness, or hopelessness, etc. If Rescue doesn't work as well as you might like, maybe try one of those. Holly might work, Rock Rose, Star of Bethlehem, maybe Vine - if she's trying to dominate or be inflexible.

There are like... 38 essences in all, here's the site if you want to look at them: http://www.bachflower.com/38_Essences.htm

Though the collar thing would be a good thing to also add to it, maybe. It's always great if you're treating something from more than one angle. I would say get her counceling... but... I don't think any human would be able to understand her problems :P