RB knew this was not their first kiss because when they were little they had kissed, the kind of sweet kiss that children do. She was very impressed with it and dreamed of it as the most beautiful moment in her life.
After she grew up she was curious about the real kissing sensation, the intimate kiss like adults. But she was too lazy to do it with anyone, besides she still hoped to be with Viscount Darwin again.
However, after his unpleasant treatment, the way he saw her for the first time after they had not seen each other for a long time hurt her. And even it made her sick of all kinds of skinship with men, including kissing.
Quite a several leaders of the bandits, as well as several assassins, tried to get close to her. But she always wasn't interested. One of the reasons was that she was still expecting Viscount Darwin's presence, even though she was not fully aware of it. Her subconscious explains it all.