The Women in the Life of Roman Emperor Caligula

The reviled emperor Caligula paid the women in his family singular honors. His coins were the first issued devoted entirely to a woman, Agrippina the Elder. Caligula's three sisters were named on sesterii from A.D. 37-38. His sisters and grandmother Antonia Minor were the first to be honorary Vestal Virgins. Caligula's sister Drusilla was the first woman to be named in an imperial will as heir to the emperor's power (imperium). Drusilla was also the first woman to be deified.
Source: "Diva Drusilla Panthea and the Sisters of Caligula" Susan Wood American Journal of Archaeology, Vol. 99, No. 3. (Jul., 1995), pp. 457-482.