Bad Hair Color at Salon - Continued!

I posted a previous message about having lowlights added to my light blonde hair at a salon. They turned out terrible and so the stylist removed them. She left my hair very light - almost white, with some light yellow and light orange where the lowlights were. I was afraid to let her do anything else to my hair so I went to another salon and they put an ash blonde over it to give me some color and cover the yellow and orange. It turned out pretty good, but I would like to go back to more of a light natural blonde shade that I had before the low lights. Does anyone have any advice on whether I should try to dye over the ash when my roots grow out? I am concerned that it may turn a strange color because of the ash and/or it will bring the white, orange and yellow back out. I have spent so much money at the 2 salons and can't afford to have anything else done professionaly for a while. Any advice would be greatly appreciated!