And the Senate had every right to vote her down if they didn't like her
The Senate Judiciary Committee most likely would have voted her down. Pres Bush did not ask her to withdraw and neither did anyone I personally know -- our State GOP Chairman even said it would have been better if she went through the hearings.
IMHO this was her personal decision after her visits to key Senators and her lack of response to fairly easy questions from what I have heard. I don't think she was prepared for the hearings, her writings were against her, and all in all she did what she thought was the best thing for the President and that was her decision to withdraw.
I would have preferred she go through the hearings but I don't walk in her shoes. I just don't think she was thoroughly vetted and her response to Senators whose support she needed was not very good.