Again for new trikers - something I never noticed that my wife brought to my attention. She was getting thrown around on a very uneven road, I didn't notice it near as much.
On a 2 wheeler you may get some pitch - a see-saw action along the direction of travel. If you watch motorcross it is very obvious. On a trike there is also a lateral axis we deal with when one wheel hits a bump different from the one on the other side. This causes the trike to roll side to side. If you ride against a backrest (as Gloria was doing) you also can be tossed side to side, and to a lesser extent, fore and aft. The trick is to let the trike move under you while your body stays upright. The trike piviots under you with the "hinge point" at the seat to sadde interface. She was keeping her back hard against the rest and that was tossing her sideways. She now (and I seem to always have - didn't think about this until she brought it up) sits lightly against the backrest on rough roads and lets the trike move around under her. Hope that makes sense.