Yoona-939 ascended before Sonmi-451 and guided her out of ignorance into a world of knowledge. She shares all sorts of secrets with Sonmi, from pureblood technology to picture books, and this makes Sonmi dream of a world outside of Papa Song's.
However, even though they're living hundreds of years in the future, this is a tale as old as time—the beginning of time, in fact, with Genesis in the Bible, where knowledge is a one-way ticket out of paradise. Taking knowledge is a one-way ticket out of Papa Song's, too, though Papa Song's is hardly Eden. For Yoona-939, that ticket comes in the form of a few dozen bullets, which kill her when she tries to escape. What is it with Supreme Beings not wanting people to have knowledge?