The level of assault charge used, up until 'Section 20', is determined solely by the level of injuries sustained by the victim. i.e. 'Common Assault' merely requires 'the infliction of unlawful force', 'ABH' requires that the injuries be 'serious' and 'GBH' [under Section 20] requires that the injuries be 'really serious':
https://www.cps.gov.uk/legal/l_to_o/offences_against_the_person/
'Section 18' requires BOTH that the injuries be 'really serious' AND that the aggressor intended to cause such really serious injuries.
So, if there's no doubt that the injuries sustained by the victim were 'really serious', the Crown Prosecution Service will now have to consider whether they can still show that your daughter caused them AND that she intended to do so (in which case they'll pursue a Section 18 charge) OR simply that she caused them (without the evidence of intent, in which case they'll pursue a Section 20 charge). Unless the level of injuries can be shown to be less than 'really serious' there's no chance of a lesser charge (such as 'ABH') being used.
Of course, if the CPS is left with insufficient evidence to obtain a conviction on ANY charge, they'll be forced to drop the case. However it's the policy of the CPS to pursue assault charges (wherever possible) even when the victim retracts their statement as:
(a) it doesn't change the fact that the law has been broken ; and
(b) to do otherwise would effectively be an invitation to attackers to pressurise their victims into withdrawing their statements.
Further, a 'retracted' statement can still be used in a prosecution, with the victim being required to explain to the court why he longer supports that statement.