Cord leader Raila Odinga's daughter was flown out at about 11am on Tuesday accompanied by neurosurgeon Oluoch Olunya and Amref flying doctors.
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It is not yet confirmed which hospital she was taken to but sources indicate she had been flown to South Africa for rehabilitation.
Reports earlier revealed, Rosemary had meningioma, a brain tumor that is not life-threatening but applies pressure to the brain.
According to the source, the tumor had caused her to bleed internally before she was rushed to Aga Khan hospital.
Last week after the diagnosis, she was being examined by two surgeons who were to decide whether to perform the surgery or not.
Doctors were only able to stop the bleeding and did not perform the operation.
A meningioma can cause blindness, problems with movement and multiple other complications as it grows and presses into the brain
Meningioma is often slow-growing and has no immediate symptoms making it hard to detect, it usually does not require immediate treatment and the good news is as many as 90 per cent are benign (not cancerous).
Leaders across the political divide in a rare show of unity have wished the ailing daughter of opposition chief, Raila Odinga quick recovery.
Nairobi gubernatorial aspirant, Miguna Miguna, a once close ally of Raila wished Rosemary quick recovery.
Former Gatundu MP and Narc Kenya chairperson, Martha Karua sent a heartfelt get-well message to Rosemary as she recuperates.
" Get well soon my dear, I'm praying for you,"Karua wrote in a tweet.