Sonja Suder, 79, is suspected of belonging to the Revolutionary Cells group in the 1970s and supplying weapons and explosives to a commando led by militant mastermind Carlos the Jackal for a hostage-taking at the meeting in Vienna.
Three people were killed including members of the Iraqi and Libyan delegations to the Organization of Petroleum Exporting Countries as well as a police officer.
Convicted militant Hans-Joachim Klein has accused Suder of recruiting him to take part in the bloody Vienna siege.
She has been charged with three counts of murder and one count of attempted murder.
Suder's 71-year-old partner Christian Gauger is also in the dock, accused of taking part with her in several explosives or arson attacks in German cities.
The pair had fled to France in 1978 and were arrested there in 2000. Extradition to Germany was requested a year later.
But France's highest administrative court in December 2010 quashed the pair's bid to block extradition to Germany, clearing the way for them to be handed over last year.
They received a long round of applause from supporters as they entered the courtroom in the western city of Frankfurt.