Purple Shampoo for Karla Choppette (Shadow High)?

Hi All. Id like to dye Karla's hair to a silver/grey and Im going to try the grey hair shampoo method (the ojes with purple undertones). Anyone have experience with using these types of shampoos that can sugfest the best brand? It probab wont work as well as she already has light hair but Im sure i will like the result regardless!

As a side note - has anyone used the dye from this company (sadly they arw out of stock of grey which is typical)