Isn't it usually the university that makes the offer to the student? I wonder how many offers she got.
In the United States, students apply to colleges they're interested in and choose from among those that accept them. Schools don't extend acceptances to students who haven't applied, even if they're celebrities. But, if a celebrity applies, many schools will bend their standards to accept them.
Williams is among the most competitive schools in the United States. Unless Eugenie is an exceptional student, she'd be in way over her head, if they did admit her.
(I have no idea whether she is or isn't a good student. We don't have anything comparable to A levels and B levels here, and classes like art and art history, two of the subjects she tested in, would be considered pretty lightweight electives in high schools here. Colleges like Williams demand all-around excellent grades in English, advanced math, science, history, and foreign languages.)