Should I speak up or stay silent

So a while back I was talking to one of my friends and he says he always wanted to play the organ(piano) and I had got the idea of him being dressed as a vampire as the day went on I started to think what if my whole friend group was a band of vampires who’s stuck there and have to sing to find their way back home so I told this to the whole friend groups and I even gave character designs/ descriptions and one of my other friends has low-key taken it and made her vampire character Her Oc and I didn’t mind but I feel like she’s taking over my idea and I don’t want to seem like a bitch by saying she can’t do that but I also don’t want my credit and idea stolen so should I ask her to give me credit when she posts anything related to it or should I not say anything