All Over Color-Partial Foil

I've had my hair colored many times and by different people.  There have been two colorists that I really like, but they have left the state so I'm back at square one.
The last person who colored my hair did a decent job, but I'm confused about her technique.  Since my hair had previously been colored (partial boliage), she wanted to do an all-over color and partial foil.  She did the all-over first, washed, then dried.  After that is when she did the partial foil.  The time or two I've had that done before, the colorist did them at the same time, making sure the hair that's going to be foiled did not get the all-over color.  It seems like with her process, it does more damage than good, especially for my thinning hair. 
So my question is, what is the correct way to do an all-over color and partial foil?
Thanks.

karen s wrote: Well different stylist do it either way, I do both at the same time,(foils & colour) as you have said the other way does cause more damage to the hair. Think about it, she used developer to deposit colour onto your hair, then she will have to use a 40 vol developer to lift the colour back out of your hair in the foils, therefore cause more damage to the hair, so you are right to be a bit concerned.   I hope this has answered your question, Karen