Difficult Color Correction - advice please!

I have a client - natural level 3.  She had her hair colored all over with a level 2 (unsure of color line/exact shade) about 6 weeks ago.  Now, she wants to go bright aqua blue on the top half of her head, with the bottom half remaining the level 2 so the black is peeking out under the blue.  Problem is, we tried to bleach it out and after 2 hours it only came up to red/brown.  So we re-colored it with Schwarzkopf Igora Royal 3-0 so at least her hair was the same color all over again.  I'm thinking that a color remover would work so that we can work with her natural hair and bleach it out to pale yellow but have never used one before - any recommendations on which one works best?  Also, having a hard time figuring out a formula that will give her the bright aqua she's looking for.  Any suggestions?  I have no preference for color lines but use Schwarzkopf Igora Royal regularly.  Any help much appreciated!