New client covering 90% grey roots

Hi, I have my first client who has had goldwell colours previously and I'm using L'Oréal. She had a permanent 6NA on roots and semi 6RB on lengths and ends (which was apparently a little too red) But she likes the slight red tone.

Can I please get some help on what to do with L'Oréal Majirel and richesse? She's 90% grey and a natural base 5 on 10% of hair.

I am thinking I need 1/2 base 6 + 1/2 dream shade say maybe 6.53 for roots for 17 mins then emulsify with warm water and take through ends for 17 mins?

I'm a little unsure of best colour to use and if I can just do a permanent this time as otherwise I'm spending a fortune on several colours...

Thanks for your help!

Here is a pic of her current colour that she's happy with