For what purpose does she marry the man she considers society’s most despicable representative?

After the Temple is built, Toohey writes that its existence degrades religion, and the owner, Stoddard, sues Roark. He loses the lawsuit, and Dominique's testimony for the prosecution is so strange, so weirdly supportive of Roark, that she winds up being fired from the Banner. To punish herself, Dominique proposes immediate marriage to Peter Keating, who agrees, despite the fact that he was finally supposed to marry Catherine Halsey the next morning. Their marriage is hollow and cold.