You could talk her out of it --- the only person I do these kind of highlights on is my mom-- she loves it, and I have to sneak an inbetween color in there sometimes to please my eye.
If she hasn't been blonde before, all the reason to try talk her into something more natural, that will grow out nicer. Toning isn't always good, because it doesn't last very long. Look at her eyes, if they look caramel it should match that, IMHO.
I have talked people to a much softer color, having them like the results and be grateful they didn't go that route. It's the really young ones that see pop stars change their hair color on a weekly basis that think they can too. I had one teenager that kept insisting on me frying her hair with the blonde, her hair was breaking in my chair as I was consulting with her and I wouldn't do it. I saw her later at a restaurant with much lighter and uhm, less hair than I remembered and thought, thank goodness that's not my hand on her head.
Find out what may be going on in her life too, I have found 100% when a client wants to go drastic like that there is some kind of drama going on, all the more not to do it.
Make sure your consultation covers your a** completely