"Angela Merkel's presidency unraveled all of sudden." would be correct, if she were President. But she's the Prime Minister. How can this sentence be corrected, using a neat, appropriate expression (not necessarily one word, if not available.)
"Angela Merkel's premiership unravelled all of sudden."
"Angela Merkel's premiership collapsed all of sudden."
"Angela Merkel lost her premiership suddenly."
"Angela Merkel lost her premiership suddenly, because..."
premiership noun 1 The office or position of a prime minister or other head of government. ‘candidates for the premiership’ - ODO