right, you cannot go blonde just like that! If she has a lot of red in her hair, she will go ginger, lol i did it myself as a teenager! mortified! The red pigment in her hair is strong, it wont just go blonde,!
She needs to colour it back to brown! She obviously has red in there so it should be ok but i would advise her to do a strand test first just to be on the safe side,If she really wants to go blonde, she needs to strip any red from her hair which means bleach! then tone after. Always best done by the proffesionals!