Common App Essay Help

So I wanted to write about the prompt about transitioning from childhood to adulthood and my idea was to write about how when my sister was diagnosed with a learning disability and an anxiety disorder I had to step up and help her a lot and how this changed the way I view things and and things like that but I’m not exactly sure how to approach this. I know I need to be careful of making the essay about me not about my sister so I was looking for some advice. thanks in advance!