The problem is that the plaintiff did not only allege harmful conduct, she also alleged lack of consent. Which she had to do, because assault and sexual battery both include lack of consent as elements of the claim to be pled and proven. Consent cannot be an affirmative defense (new matter, admitting facts in prior pleading, show cause why they should not have their ordinary effect), since lack of consent was pled in the original pleading. A defendant cannot say "yes, lack of consent (which was pled in the prior pleading), but she consented."
It can be tricky figuring out whether something is a failure-of-proof defense or an affirmative defense. It ties back to the applicable substantive law and how it defines the cause of action, but it is not always clear. So take a simple example of defamation:
1) Defamation means "D made false and harmful statements about P, causing injury"--The elements are falsehood, harmfulness, and injury, to be pled and proven by P.
2) Defamation means "D made harmful statements about P, causing injury"--the elements are harmfulness and injury. Truth is an affirmative defense, to be pled and proven by D.
In First Amendment defamation cases, substantive law adopts # 1. In private defamation, substantive law adopts # 2. Either one could make sense.
So here, consent is in the same position as truth/falsity. But the plaintiff pled her claims as if lack of consent were an element. Which seems right--otherwise any touching would presumptively be a tort, unless defendant could prove consent.