Colour suggestions?

[Lafadf87]

Hi, I was wondering if anybody can help. I currently use Wella koleston from my client. I use the root touchup of 1/4 7/37 1/2 of 88/0 20 volume. My client wants to go half a shade lighter, but I am worrying that if I go half a shade lighter her roots might become translucent. What would you suggest? Would you suggest going for 1/4 of 880, 1/4 of 99/0 with the 1/4 of 7/37, or would you try something completely different? Any help would be amazing. Many thanks