Hey there.....very pretty picture.
I have several clients who have been doing heavy highlights for years and when they want low lights or and wantin to go back to their natural it is not easy and it's a long process....it sometime takes 6 months or more for the low lights to stick in the hair again.
With highlighting you have subtracted most or all of the pigment out of the hair, it's kinda like a glass with a crack in it....for awhile the water stays in but eventually it leaks out. You can have the sections with the low lights filled or re-pigmented first before the low light color goes on but it still will not guarantee staying power. You have a week or two before color starts to fade out.
I'm sorry that there is no easy solution. I just had this conversation with a 15 year old girl in my chair last night....we did do low lights again for the second time but she knows they won't stay in long. A couple of other solutions is to cut off as much as possible and grow out the damaged parts while low lighting it won't take as long....OR get some different colors of brown low light extension pieces put in....(but that can be VERY expensive) I hope this helped a bit....if you have any other questions feel free to message me.....
Karla