He died while serving a prison sentence for "inciting subversion".
Liu Xia's brother, Liu Hui, wrote on a social media site: "Sister has already left Beijing for Europe at noon to start her new life". I'm grateful for those who cared about her and helped her all these years.
Efforts to secure Liu Xia's departure came amid growing concern over her health and state of mind, after Liao Yiwu, a dissident and friend living in Germany, released details of a telephone conversation in April in which an anguished Liu Xia said she was losing hope of leaving.
Ms Liu's departure, following a year of pressure on Beijing from activists and rights groups, comes at the end of a visit to Germany by Chinese Premier Li Keqiang, during which the two countries signed commercial deals worth more than $US23 billion ($31 billion).
Merkel had paid a visit to China in late May. She has discussed Liu Xia's case with Chinese officials. Chinese officials told reporters she was free to do what she wished, but Western diplomats and the press were effectively banned from visiting her.
A Chinese foreign ministry spokeswoman, Hua Chunying, confirmed Tuesday that Liu had left for Germany, saying she was seeking "medical treatment on her own accord".
Cruz previously authored a resolution honoring the life and work of Liu Xiaobo and in July of previous year, as well as the fall of 2015, delivered speeches calling attention to Liu's plight.
"I'm in a sea of joy", said veteran activist "Long Hair" Leung Kwok-hung as he drank a toast to her.
Facebook faces record fine over Cambridge Analytica scandal
Facebook also received a minor fine of $164,000 from French regulators for failing to meet the country's data protection rules. Facebook "will get a chance to respond to the proposed penalties before the ICO releases a final decision", Bloomberg reports.
Since President Xi Jinping took office in March 2013, China's government has tightened its control over society and stepped up its campaign against independent activists, lawyers, and others deemed a threat to the Chinese Communist Party.
He was last arrested for his role in creating Charter 08, a call for political changes in China.
The Chinese government permitted the blind, activist Chen Guangcheng to travel to NY after he escaped from house arrest and hid for six days in the U.S. Embassy in Beijing.
Several expressed concerns about the fate of Liu's brother, Liu Hui, who has previously been convicted of fraud and sentenced to jail in a case supporters said was a form of retaliation against the attention the Nobel laureate was getting. Supporters said this was done because of the attention Nobel victor Liu Xiaobo received.
While news and information about the couple are strictly censored in mainland China, people in Hong Kong took to Facebook to send their good wishes to Liu Xia.
"We are disturbed by reports of the deteriorating health of Liu Xia".
But for nearly a year that wish has remained out of reach, as she has remained under house arrest in her residential compound in Beijing, where friends said she was losing her will to live.
"We call on the Chinese Government to permit Liu Xia's brother, Liu Hui, to travel freely and to release all other political prisoners".
In the past year since her husband's death, authorities continued to closely guard her home, allowing only a few friends and family members to speak to her on the phone or visit her. Liu Xia is reportedly suffering from severe depression and a range of physical ailments, including a heart condition. But Liu said she had not expected to be kept under house arrest.