The Downton Abbey star, 34, wore a flowing, mustard yellow Cushnie Et Ochs gown for the event, with her hair down in loose curls. She posted several stunning shots from the evening on Instagram.
“Headed to #nerdprom2016,” she captioned a black-and-white photo of herself laughing while in the backseat of a moving car. “#whcd #joy.”
“Nerds,” she captioned the photo simply.
Dockery has remained largely out of the limelight in recent months since Dineen died from a rare form of cancer in December at the age of 34.
The PR professional from Ireland had been working in London when he learned of the diagnosis, and returned home for hospice care and to spend more time with his family in his final days.
The pair reportedly got engaged in February of last year after more than a year of dating.
“I was honored to know John, to love and be loved by him,” the Good Behavior actress said at his funeral in December. “He was my friend, my king, my hero, my everything. We celebrate him, we honor him and we will miss him.”
For access to all our exclusive celebrity videos and interviews – Subscribe on YouTube!