OP, if you do NOT want this to happen, she can go through the name update process in Pakistan. She will need to post in the newspaper for two weeks, and then take those newspaper clippings to NADRA, where they will update the record. You need to keep those clippings with you for the 20+ years so I suggest you scan them.
You can prove that you two are siblings by submitting your birth certificate and your sibling's, and the documents will show both parents' names