The D's lack of experience goes to the essence of the plot.
I was taught by my mum (an earth-mother type) in my early teens when I exhibited obvious interest in female "intimate" parts :if a male makes his feelings known to a female [easy-peasy as I was to find females just "know" a male's wishes on sight], the female should usually give a gentle but firm "no" ("this is not appropriate" was what I'd hear over and over). The male, unless his little guy had a rampage, would back off.
Trust is vital. The girl herself, and often her anxious parents, would have to trust the male escort enough ,~100% certain, that he wouldn't force her.
No sex-ed is needed for this.
In DMD, if D were to say "enough is enough" (and indeed she has) and MC backs off cursing himself for his own folly--end of story.
If MC says "You little slut! You won't tease me again!" and rapes her--end of story.
There is no truly plausible storyline. Society (and older women) usually teach young girls not to give males "opportunities". Increase the opportunities, lessen the surprise. For D to sleep naked in MC's bed is just WTF!
But I really don't see many alternatives to advance the story (other than date-rape or assault-rape which thankfully won't happen).