Always ends up brassy

I have a client that is a level 6 and about 40% grey. She wants to be a neutral level 8 blonde. I have tried an ashed based color, a purple base and a blue base, and each of them still bring her up to a brassy, orange level 8. I've tried toning it afterwards and it still stays orangey. Does anyone have any tips on what I could do to just neutralize this orange? I have run out of ideas! Everytime I do her hair I sit and ponder possibilities and formulas even to the point where I lose sleep! Thankfully she's been patient and knows her hair stubborn.:)