Here is how to mirror a pose in Daz3d:)

1. Have the figure you wish to mirror selected
2. Either navigate to the symmetry button from the Parameters tab or hit Shift+y to bring up the Symmetry options box.
3. To mirror a full body pose as you described the settings should be as follows:

Nodes: Selected
Propagation: Recursive
Direction: Swap Left and Right
Trunk Nodes: Mirror YIZ rotations

Left node prefix: left;l
Right node prefix: right;r
 
Transforms: Check the x, y, and z axis boxes

Leave all other boxes unchecked

Happy mirroring :)