You are talking about 2 very different things here. A retraction statement is one which says "I made a complaint to the police on .... regarding being assaulted by ..... I have now reconsidered the matter and have decided that I do not wish to persue the matter. No one has asked me or put any pressure on me to withdraw my statement, a decision I have made alone" or words to that effect. The second option is far too dangerous to even contemplate. If she subsequently makes a further statement saying that the injuries were not done by you, she is making a false statement. Once she signs the declaration at the top of the statement she is committing a criminal offence. Charges of Attempting to pervert the course of justice or perjury could ensue.
I have rarely seen an assault case ru at court without the cooperation of the IP (injured party). Inder certain circumstances, CPS could ask the court to deal with her as a whats known as a "hostile witness", This means that she can be physically placed before the court and asked to give evidence. THIS RARELY HAPPENS. CPS are most likely to offer no evidence on the day of court and the matter will be over. The best advice, in any case would be to keep your hands to yourself in future.