I think it's her challenge in this life, she might have to experience in oppose race this life time to balance her karma wheel. If she was a racist in past life & beat/ molasted ppl from oppose race, there's a big chance for her to learn the same experience as a victim. It's for her & those surround her to understand of being better human; acceptance despite of different race.
She might have known this would be her next mission of life as she has given a choice to pick her white parents with her siblings. I do believe nothing is coincidence, everything is pre-destinied to maximize the spiritual evolution. However, successful in her mission or not, depends on her. If she masters things that she supposed to do & evolve, her soul is improving.
The impact wouldn't be completely in vain (my opinion), thru her, there's connection in 2 different races, make people aware of reincarnation in different races; thus, human shall not discriminate to each other due to ethnic, skin color & gender.
Her reincarnation in this life DID gave lesson to herself, her family, ppl surround her & those who read her story.