Can I move my 22 year old, mentally disabled niece from (whom I do not have legal guardianship over) from a mental health group

If you are not appointed as her guardian or guardian advocate under Florida statutes, it is highly unlikely the facility will permit you to remove her from the facility at all. You can apply to be her guardian or guardian advocate . Florida statutes have provisions for doing that in the case of a mentally disabled person without having to have the customary three person panel appointed to determine her capacity. The statutory regimen was designed to permit persons interested in handling the affairs of adult individuals who are developmentally disabled to pursue that goal at somewhat less expense and paperwork than the traditional guardianship path requires. I would not advise your moving her without authority from the court to do so. Where are her parents, because they would normally be the most interested parties in her welfare and well being. You have not stated whether she has siblings or parents still living, or why they are not involved. If you wish to pursue this, you should hire an attorney experienced in guardianship work in the county where your niece resides. Best of luck to you on it!