Answer:
Your first paragraph (after intro) can introduce the struggles you faced when your parents paid your baby sister more attention.
Your second paragraph can be about little moments you enjoyed with your sister, where you found yourself really caring for her and realizing why she may need more attention because she's younger.
Your third paragraph can be about how you have realized that you are loved and cared for, and how much you love and care for your sister.
I would write it out, but I feel uncomfortable writing about someone/an experience that I know little about. I hope this helps! ❤