Can I bleach again or just live with it?

Hi all

3 months ago a friend put highlights in my hair (over previous salon foiled hair). She did a bad job. 2 weeks later I put a permanent dye over (John Frieda 9N Light natural blonde). 4.5 weeks ago I had my hair bleached. The roots and the highlighted bits went well. The underneath was done twice and was still quite dark (think light orangey brown). Not quite a week ago I had my roots bleached again. Looks great when toned. The underneath wasn't done. The hair stylist was a bit preoccupied (sick kids etc). Question is can I just bleach the darker underneath again or did she not do it because she thought my hair would be fried?!? My hair is in quite good condition. And if I do it should I do a bleach bath or just bleach away and check it carefully? The underneath is darker be said of the previous dye I put in. (I want my hair 'white'/ very light ash and I like how it grabs the purple).