[West side of the Ara Pacis, 9 BCE, source: Wikimedia Commons]
The Flaminica Dialis, and presumably the Regina Sacrorum as well, primarily assisted her husband with the rituals he performed. Plutarch suggests that this assistance was essential, but the way he says it also implies that it was so commonplace that most would not comment on it, while Aulus Gellius tells us simply that “The ceremonies of the Flaminica Dialis are about the same [as those of her husband].” In addition to this, however, they had their own responsibilities. Each nundina (market day), the Flaminica Dialis sacrificed a ram to Jupiter. On the Kalends of every month, the Regina Sacrorum sacrificed a sow or female lamb to Juno. They also participated in larger religious rituals and observances as well, for example the Argei, for which the Flaminica Dialis was supposed to wear her hair uncombed and unarranged. Presumably they had other responsibilities as well, but the sources don’t tell us what they might have been.
These women also shared many of the restrictions imposed on their husbands and had their own distinctive clothing and hairstyles reflecting their positions. Aulus Gellius gives an extensive list of what the Flamen and Flaminica Dialis could not do, adding that the Flaminica could not go up a staircase of more than three steps, presumably so as not to expose too much of her legs. Perhaps the strongest indicator of how important these priestesses were is the fact that the death of either husband or wife meant that the other had to step down. Remarriage and divorce were forbidden. The loss of one spouse made the other incomplete, and therefore unfit for this high office.
Aulus Gellius, Attic Nights X.15 - Lacus Curtius
Macrobius, Saturnalia I.15-16 - Lacus Curtius (text in Latin)
Plutarch, Moralia, Roman Questions 50 - Lacus Curtius
Maurus Severus Honoratus, Commentary on the Aeneid IV.374 - Perseus
Flamen Dialis - Wikipedia
Rex Sacrorum - Wikipedia