First I must say please dont let people who make judgements on your choosing to continue coloring your hair make you feel guilty or badly. Now that being said most woman will agree if a little thing like hair color or makeup, shaving your legs ect, makes you feel better about yourself during an obviously stressful time, you go girl!!!!
Enough of that I have been using Clairol Root touch up. Because I have also highlighted for years and have three blended colors, I have been using 3 colors of the touch up. As your hairdresser does, just alternate the colors trying not to blend them. Hair always colors better dirty, I think it helps stay separated to assure a better out come. It only last two maybe three week for my hair (because I am white in places, too many places :))but my bbf uses it and it lasts her 5 weeks or longer if she stretches it. I buy it at Target and Longs when it's on sale. It's like 5 or 6 dollars.
I believe a woman named Kristin responded and said she is a hairdresser and told you to speak to your h/d directly, I thought that was very good advise and hope you take it. Good luck and good hair to you. :)