When Antoninus died on 7 March 161, Marcus and Lucius Verus ascended to the throne and became co-rulers.
Faustina then became empress.

Not much has survived from the Roman sources regarding Faustina's life, but what is available does not give a good report.
Cassius Dio and the unreliable Historia Augusta accuse Faustina of ordering deaths by poison and execution; she has also been accused of instigating the revolt of Avidius Cassius against her husband.
The Historia Augusta mentions adultery with sailors, gladiators, and men of rank; however, Faustina and Aurelius seem to have been very close and mutually devoted.

Faustina accompanied her husband on various military campaigns and enjoyed the love and reverence of Roman soldiers.
Aurelius gave her the title of Mater Castrorum or ‘Mother of the Camp’.
She attempted to make her home out of an army camp.
Between 170–175, she was in the north, and in 175, she accompanied Aurelius to the east.
When Antoninus died on 7 March 161, Marcus and Lucius Verus ascended to the throne and became co-rulers. Faustina then became empress.
Not much has survived from the Roman sources regarding Faustina's life, but what is available does not give a good report. Cassius Dio and the unreliable Historia Augusta accuse Faustina of ordering deaths by poison and execution; she has also been accused of instigating the revolt of Avidius Cassius against her husband. The Historia Augusta mentions adultery with sailors, gladiators, and men of rank; however, Faustina and Aurelius seem to have been very close and mutually devoted.
Faustina accompanied her husband on various military campaigns and enjoyed the love and reverence of Roman soldiers. Aurelius gave her the title of Mater Castrorum or ‘Mother of the Camp’. She attempted to make her home out of an army camp. Between 170–175, she was in the north, and in 175, she accompanied Aurelius to the east.
Faustina the Younger