Puberty

So my oldest daughter is going to turn 8 next month but I noticed that she already is just starting to develop breasts. I know I need to sit down and have a talk with her and I’ve always been completely honest about anything she’s ever asked me but it’s so hard because I still see her as my little baby. She is the sweetest person I know but she is still so completely innocent, for example her brother was talking about he saw someone give someone else the finger and she’s like how is that bad so I asked her if she knew what that meant and she said yes and she pointed at me. I didn’t start developing until I was 10/11 but I grew up very different from her and already knew a lot about everything. When do you think would be a good time to have a conversation with her about her already changing body and how do I put it to where she is still informed but that she still keeps her innocence in some sense