Stephanie Meyer did what J.K. Rowling did with the "Harry Potter" series, and made reading fun and cool again. For a long time now, reading has been declining severely. If you are perceived as reading too much, you are considered a nerd, bookworm, smartypants, goody-goody, or a suck-up. With Stephanie Meyer and her "Twilight" series, it became cool, fun, in, and hip to read. All of a sudden the tables were turned, and if you WEREN'T reading her books, you were the nerd, left-out, and ostracized. So, she really made reading-and literature-come back into style.
Another thing that she did was use literature to inject new life into the vampire mythology. She brought vampires to a teenage level of understanding, made them decent, protective, gentlemanly, vegetarian, and very much NOT like the evil, blood-thirsty monsters that vampires have often been portrayed as in the past. She really humaized vampires, and continued the vampire obsession in the new generation. She made literature-and not movies, as it has been for so long-the new medium for vampire tales.
One last impact that Stephanie Meyer has had on literature is making it accessible and likable to all ages. Before, if your daughter was reading some teeny-bopper book, you would have no interest in reading it. But the "Twilight" series was appealing to readers of all ages, at all reading levels, and of all types. In that way, Meyer has brought reading to masses of people, and connected them with a common love. She has used literature to bond people together, give them a commong ground, and forge friendships and connections.
I hope that those ideas get you started, and help you come up with some thoughts that could work as a thesis. Good luck!