Help with changing highlights to balayage

[MollyB123]

Hi i have a client tomorrow who usually has a half head of lowlights and highlights. Would say she is base 5 with little grey. She wants to have balayage instead so i wanted to have advice on whether to precolour and what to use, i normally use loreal colours. Was then going to go in with some babylights with bleach and 20vol, roots with ash brown maybe 5.1 as she doesn't want any warmth and take some of this through to the ends and then bleach a few of the ends with 30vol. Will probs tone with ashy toner perhaps 9.01 but will see how it comes out first. Just wanted to see whether people would bother to precolour as shes got warm colours in her hair already but I'm worried about the base colour going over the previous blonde highlights. Don't want it to look wishy washy. Have attached picture of her current colour although not very clear lighting ,sorry! Have also attached the colour we're aiming for. Any help or advice would be great! Xxx