Mother with a teenager who experiments a lot with color

How about parental control...

What exactly is the question? Specifics are important.

I am a mother with a teenager who experiments a lot with color.
For her soccer season she often colors her hair purple (the team color).
We used a purple Splat product. The color did not take as well as we'd have liked and quickly within two weeks has faded to pink.
So, she decided she weanted to put it back to her natural color which is very close to what we purchased, Loreal Superior Preference, Med Blonde Natural.
Now much the pink is spotty on her head and the ends, turned a ashy blonde, almost gray in some parts.
How do we even out the color? Can we try to colr over it again? Does it have to be stripped and then recolored? I love in a rural community with limited selections for beauty products. Can someone recommend a product that is available at a Wal-Mart or Rite-Aid?
Thanks, she is really unhappy about the current look of her hair. We'd like to correct this tonight.
glassgirl