You must learn to add more context related material when asking this kind of question. How it is used in the overall text can help in determining how best to answer your question.
"Which girl do you want to transfer a package to?"
More likely than not you mean, "Which girl would you like to send the package to?"
Although what you wrote, might me grammatically correct, it wouldn't be easily understood. The sentence could indicate that you wish to take a package from one girl and send it to the other.
Student or Learner