Think about what potential triggers are involved to cause someone to get 'horny'.if you never had it wouldn't you wanna do it more and be horny?
They can be visual / chemical stimulants that cause the body to react in particular ways, but these types stimulants effect different people at different levels of intensity, and some people not at all.
They can be based on previous experiences and the desire to want more, but that requires previously having those experiences. Studies have shown that some people have never masturbated, no matter how old they were at the time of the interview.
They can be based on wanting something that either others have or have experienced, but that requires knowledge of the things you have yet to experience. This is one potential possibility for D as she has a friend that talks about sex so it would be possible for D to want something that she does yet have, but she might be waiting to find the 'right' person to learn these things with.