Sibling not bonding with new baby

So I have a 12 year old boy who has been great with his baby sister.. he wants to hold her, talks to her, helps if she cries, feeds her too. I also have a 9 year old girl who on the first night home wanted to stay at a friend's house and hasn't been too interested in holding or pay much attention to her baby sister... I've talked to her asking if she feels left out and asked how she is feeling and she only said she is fine and she loves her baby sister 🤷‍♀️ Am I thinking too much into this or has any1 else had this happen? What did u do to help them bond?