R. Feinstein on a Disputed Marriage (20 Adar Sheni)

שו"ת אג"מ אה"ע א:פ"ט 20 Adar Sheni 5711 (1951)

A fifteen-year-old gets pregnant, and has a quick marriage. Except that she claims that the husband used a different woman as a stand in for her, so there never was a marriage. What's the ruling?