Eimear Walsh (21) was a third year medical student at UCD, as was Lorcan Miller, another of the students who died. She had attended Loreto College Foxrock until 2012.
Loreto principal Bernadette Prendiville said in a statement on the school's website: "We in the Loreto College Foxrock community are deeply saddened and shocked by the events that took place in Berkeley, California.
“We offer our deepest sympathies to the families of Olivia [Burke] and Eimear, and to the families of the other students who died. Please keep in your thoughts and prayers all those who have been injured and affected by this terrible tragedy.”
Both former Loreto girls had been working as hostesses at the Hana Zen sushi bar and Japanese restaurant overlooking San Francisco Bay at Pier 39.
Restaurant owner Alvin Louie told local media they were “hard workers and very sweet”.
The restaurant held a candlelight vigil in their memory.
Mr Louie said Ms Walsh was on the verge of promotion.
His wife, Angie Louie, said: “They were quick and smart. They were always smiling, enthusiastic and full of energy.”
UCD has opened an online book of condolence. The college’s president, Prof Andrew J Deeks, extended condolences to the families and friends of the dead and injured.
“We cannot comprehend the desperate shock and grief they are feeling and we are heartbroken at their suffering and loss.
A minute’s silence was observed at conferring ceremonies on Wednesday.
There will be a memorial service on Friday at 1pm in Belfield Church.
"Our students, like thousands of others across Ireland, head to the US each summer on J1 visas to enjoy the experience. It is heart-breaking to imagine that such a tragedy would strike these wonderful students when their lives are opening up to discover the world," Prof Deeks said.