Maybe a sister was caught doing a very sensual dance in her own space. She was expressing herself through movement and was discovered by her sister who initially thought she was doing something inappropriate but then realized it was just her way of art. So they ended up having a conversation about self - expression and creativity.
It could be about a sister being caught wearing a really fashionable and alluring outfit that she wasn't supposed to wear outside yet. For example, a new red dress that was too 'grown - up' for her age according to her parents, but she couldn't resist trying it on and got caught by them.
A sister might be caught writing a love letter that was very passionate. She was pouring out her feelings for someone she liked. When she was caught by her older sister, she was really embarrassed at first. But then her sister comforted her and gave her some advice on relationships and how to handle her emotions in a proper way.