The 'She's The Man' actress has worried her parents Rick and Lynn so much with her bizarre recent antics that they visited several lawyers in a bid to sign over all legal, medical and financial control of her affairs to an external party.
The troubled star was booked for drug possession on Thursday evening when police visited her New York City apartment after receiving a report of a disorderly person.
Amanda - who was spotted smoking a joint in the lobby and behaved erratically throughout the incident - was taken to hospital for a psychiatric evaluation, before being arrested for criminal possession of marijuana, as well as reckless endangerment and felony tampering with evidence when she attempted to throw a bong out of the window.
Her parents' attempts have been unsuccessful so far, however.
A source told RadarOnline.com: "Rick and Lynn have met with several lawyers that handle conservatorships in the past month, because they want to get a conservatorship of their daughter. They have been advised that even as disturbing as Amanda's behaviour is, it's very unlikely that a judge would sign off on a temporary conservatorship.
"Conservatorships are very hard to get, and being mentally ill and addicted to drugs isn't enough. Amanda hasn't ever been to rehab or ever agreed to see a mental health professional. Her parents are absolutely powerless to do anything at this point."
In recent months, the 27-year-old actress alienated herself from her family by moving from Los Angeles to New York when her parents confronted her about her actions, which had resulted in several altercations with the law.
She is currently on three years' probation for driving with a suspended license and has a driving under the influence (DUI) case pending in Beverly Hills. Amanda also previously settled two hit-and-run cases after reaching a civil compromise with her victims.
The insider added: "This latest arrest has broken their hearts and they are sick with worry, but there is nothing they can do under the law."
The star's odd behaviour appears to have snowballed in recent months, with the former Nickelodeon star radically changing her appearance and posting disturbing comments about her weight on Twitter.