Tashfeen Malik, 29, studied at the Al-Huda Institute in Multan, which targets middle-class women seeking to come closer to Islam and also has offices in the US, the UAE, India and the UK, the teacher at the seminary, who gave her name only as Muqadas, said.
The institute has no known extremist links, though it has come under fire in the past from critics who say its ideology echoes that of the Taliban.
Malik and her husband Syed Farook, 28, were hailed as "soldiers" of the self-proclaimed caliphate following the massacre on Friday at a social services centre in San Bernardino.
Investigators suspect that Malik, who went to the United States on a fiancee's visa and spent extended periods of time in both Pakistan and Saudi Arabia, may have radicalised her husband.
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The teacher did not say when Malik studied at the seminary, but fellow classmates at the Bahauddin Zakariya University said she had attended the madrassa after classes at the university, which she attended from 2007-2012.
Farrukh Saleem, a Karachi-based spokeswoman for Al-Huda said, "We are trying to establish whether she attended Al-Huda as a regular student or was just a listener."
Unlike other such seminaries, it mainly targets Pakistan's influential middle and upper classes, often holding religious study circles inside members' houses.