"The donor suggested that I come and fetch the cheque at the Gupta's house in Saxonwold, and it transpired that he was a senior executive in one of the [Guptas'] companies," Zille said in her weekly newsletter published on the Democratic Alliance's website.
The Western Cape premier was responding to reports that she apparently solicited a donation worth several hundred thousand rand from the family who are known to be close associates of President Jacob Zuma.
"It was a personal cheque from his personal bank account. It did NOT come from a Gupta company, nor from the Guptas, but it was handed over at their home," she added.
Zille said she reluctantly made the details of the donations public – while still keeping the identity of the donor secret – to quash the negative and false reports on the matter.
"Ideally the DA would prefer full transparency. But if we were the only party to apply it, most of our donations would dry up – together with any prospect of sustaining democracy in South Africa," she said.
Apparently the donor refused a request by the DA to have his name made public, according to the statement. But Zille also said she would find no problem with the controversial family donating money to the DA or any other political party.
"There is absolutely nothing wrong with the Guptas giving money to any political party they choose – as long as they do not request or receive favours from a government using taxpayers' money as a reward."
The opposition leader also used the newsletter to defend her decision to pull out of a business breakfast hosted by the New Age, which is owned by the Gupta family.
She maintained her decision to do so was based on newspaper reports that state-owned enterprises had funded the breakfasts to the tune of millions of rands.
"The word 'sponsorship' is a fig-leaf for disguising the transfer of millions of rands of taxpayers' money into a company owned by the Guptas, who are major benefactors of the ANC and Jacob Zuma," she added.
Zille also claimed she was "unaware" that a New Age Business Breakfast she attended in 2012 was sponsored by parastatal Telkom.
"Apart from the fact that the government is a minority shareholder in Telkom [unlike Eskom, Transnet and the SABC], this argument misses the point," she said. "There would have been nothing wrong with an ordinary sponsorship. There is something profoundly wrong with a 'sponsorship' being used as a cover for a conduit of state funds to a private benefactor of the ANC and Jacob Zuma."