"There is a majority for centrist policies, but no majority for a centrist government," she told a press conference.
On Monday she reported back on the task handed to her last week by parliamentary speaker Andreas Norlén.
Over the past week, Thand Ringqvist has met party leaders from across parliament in an effort to explore options for a centrist coalition, aiming to get the Christian Democrats, Liberals, Greens and her own party to back centre-left Social Democrat leader Magdalena Andersson as prime minister.
However, both Liberal leader Simona Mohamsson and Christian Democrat leader Ebba Busch have remained steadfast that Ulf Kristersson, leader of the centre-right Moderates, is their choice for prime minister.
Thand Ringqvist said the parties' "red lines" remain intact, including her own party's refusal to let the Left Party into government or cooperate with the far-right Sweden Democrats.
"All parties that have red lines have to think about how to handle their red lines," she said.
She said the Centre Party would be prepared to accept the Social Democrats in a single-party government, as long as it promotes centrist policies.
It will be up to the speaker to decide what to do next. He has three attempts left to put a prime ministerial candidate to a vote in parliament before a new election is called.
Thand Ringqvist said that perhaps a centrist government would be possible in the final vote, when the parties have to choose between that or a new election.
"I still believe in a centrist government at a later stage," she said.