The former child star was originally detained under the 5150 order, which allows authorities to hold patients for 72 hours while they undergo mental evaluation.
Amanda's lawyers reportedly resisted the extension but her doctors have said they need two more weeks with the star to ensure a correct diagnosis of her mental health.
A photograph, which is believed to be of Amanda, has been leaked online showing the 27-year-old covered by a white sheet and being wheeled around the hospital grounds by a member of staff.
The Disney actress' parents, Lynn Organ and Rick Bynes, are backing the doctor's decision after an incident near their home on Monday night prompted Amanda's detention.
The troubled star was accused of being drunk, trespassing and starting a fire in the grounds of a retirement community in Thousand Oaks, California. Police were called and Amanda was subsequently taken to hospital.
Amanda's parents are now seeking conservatorship of their daughter and a hearing to decide whether it will be granted is due to take place on Friday 26 July.
Sadly, the Hollywood actress has become known for her erratic behavior of late. She has taken to Twitter to criticize family members as well as celebrities including Rihanna and Drake. She has also refused to see her family.
"You can sense there's pain and loss of control in her personal life when talking to her," said a friend.
She has also been accused of cutting off communication with former friends. "She deleted all of her email addresses and cell phone numbers so none of her friends can get in touch with her," revealed former ’N Sync singer Lance Bass.
"Her family and friends can’t get to her… so the only way into her life is through Twitter."