What brand of direct dye did you use? Has it faded much already?
Some brands stain the cuticle layer quite badly and then nothing will shift them.
There's are a few professional direct dye removers available and how well they work will depend on various factors including whether the dye has been applied more than once but don't be tempted to use a bleach mix as this tends to make a bad situation worse.
At this stage, I would be more concerned about removing the colour sufficiently than whether the remover lightens her natural colour. Some brands of purple fade out green and have to either be cut out or coloured over.