They make it sound as if she fell straight down 20 feet.. The wall is on an incline.. She probably rolled down it.. No serious injuries.. What a Do Do bird! :)
Parts of the L.A. river, particularly around that part of town, do have vertical walls.
Hollywood always shoots the part of the river that runs through downtown L.A., so that's all most folks are familiar with. That section does have a sloped embankment.