What is this type of behavior called?

my sister is a year apart from me. there's nothing wrong with me, but she acts like I need some help, trying to be nice to me. she says stuff in the morning like "good morning" in a tone thats like awkwardly gentle~~as if there's something wrong with me~~ I thought it was weird, and didnt like it, so I did it back to her recently and she doesnt like it. basically throughout the day she acts like I need special attention, like theres something wrong, basically like I need help. I dont know her motives, so i do it back to her! and When I do it back, she acts weird doesnt seem to like it. what's she trying to do? ?