Hi! First of all, thank you so much for supporting the series. I’m really glad you enjoyed it.
Regarding your question: the series is mostly SFW, but there are a few more explicit moments. For example, there’s a scene where Carmine is wearing lingerie, and another where CC is completely topless, along with a few similar scenes.
But I think the bigger thing to keep in mind is that the series deals with adult themes and topics, and it doesn’t really sugarcoat or beat around the bush. Because of that, it might be better for your younger sister to experience the series when she’s a bit older. That way, she’ll be in a better place to process its themes in a healthy way.