4 year old being odd or just anxiety?

So I have two daughters my oldest is 4 and my youngest is 6 months old. For the most part my oldest is great with her. It struck me as odd though when I would tell my oldest I was going to the bathroom she would say things like “I won’t hurt her” or “I won’t hit her head and hurt her” talking about her baby sister. Has anyone else heard this. I guess it just makes me nervous if something could be wrong with her. She just turned 4 just made me feel weird the stuff she was saying. Am I wrong just anxiety or?