The only thing she could say, Merkel added, is that things were now much better than a year ago "when I anxious a great deal more".
With exactly four weeks remaining until the September 24 election and a week before their only TV debate, Schulz and Merkel, who is seeking a fourth term, engaged in an indirect TV interview battle on separate networks on Sunday.
Over a million refugees and asylum seekers crossed into Germany in 2015 and majority stayed in the country.
"This has definitely generated some self-confidence", Merkel said.
Merkel said Tuesday that it was "important and right" that Germany took in refugees and other migrants in an "exceptional situation" two years ago but it's also important to have "long-term sustainable structures".
"I made my decision based on what I thought was right from a political and humanitarian standpoint". But Merkel, who is viewed as perhaps the most powerful politician on her continent, appeared to be calling for greater involvement around Europe.
On the future of the EU, the German leader said she backed plans to turn the European Stability Mechanism crisis fund into a full-blown European Monetary Fund.
Leclerc: Raikkonen deserves new Ferrari deal
It is a race which threatens to be hit by bad weather, but Hamilton, so often a master in the rain, is typically not fazed. Hamilton was 0.262 seconds quicker than Ferrari's Kimi Raikkonen in second, with Mercedes' Valtteri Bottas third.
The politician uses any means in his attempt to gain the upper hand over German Chancellor Angela Merkel in the upcoming election, Gavrilova wrote for Sputnik.
Mr Schulz, whose Social Democrats have been Ms Merkel's coalition partner over the past four years, homed in on her handling of the diesel-car crisis. Germany allows plaintiffs to bundle lawsuits against financial companies, and the same rights could be offered to vehicle buyers if done right, she said.
Signalling she is ready to press ahead with deeper European integration, Merkel said she did not rule out a French idea to have a common euro zone finance minister.
This centre would be in Egypt, a so-called transit country for refugees and economic migrants aiming to reach Europe.
It was only the second campaign appearance by Merkel in formerly communist eastern Germany, where anti-foreigner sentiment is especially pronounced.
"You have to live with it", Merkel said of the protests.
In the same interview, Merkel addressed critics' calls for her to come out against Trump and his demands for North Atlantic Treaty Organisation allies to ante up and contribute more to the organization's defense fund. Merkel fully backed Trump while saying relations between the two powers were strong even if she doesn't always agree with the bombastic American executive.