What ever happened, she wanted the state to have a majority stake in the bank, she told Germany's ZDF public channel.
"We can get that by taking control by means of a majority stake" in the shares, she said, adding that "as a last resort we have to think about an expropriation" of the private shareholders, which would lead to nationalisation.
Speculation has been increasing about the future of HRE bank for several weeks, the most prominent German casualty of the financial crisis.
HRE has soaked up more than €100 billion ($129 billion) in public aid since October, half of it in public loan guarantees, but its future still depends on the state becoming a major shareholder.
In a separate development, a German newspaper reported that the country's Federal Financial Supervisory Authority (BaFin) was investigating several banks over alleged insider trading surrounding HRE's collapse in September.
"The investigation is ongoing," the federal watchdog confirmed in Monday's edition of the daily newspaper Süddeutsche Zeitung.
The banks in question are suspected of having sold shares from Hypo Real Estate (HRE) shortly before the troubled German property financing group collapsed.
Several banks knew about the bank's crisis a week before its shares fell in the market, the newspaper alleges.