I was accepted to a US News top ten school. Like you, I was curious to know what got me in. My regional admissions officer emailed me a congratulations, and I replied to it asking this question. I asked so it wasn’t aggressive. Something along the lines of: Hey, I was just wondering what made me stand out among the other applicants. Some of my classmates were very qualified but did not make the cut. Was there something special that stood out? I completely get it if you don’t remember my application out of the hundreds that you have probably read.
The admissions officer wrote back with a detailed list of the things in my application that the adcoms were impressed by.
Remember, admissions officers want you to come to their school, so they would most likely be happy to respond to your questions. The committee is usually split regionally so individual officers most likely remember and are invested in the students that are accepted in their area.
As mentioned by the other posters, your sis should do what she’s interested in. But as long as she doesn’t try to copy your achievements, I think the adcom’s feedback may be helpful as points of data. Something that your sibling can look at and say: this is roughly the level of achievement that it takes. If my older sibling can do it, so can I.