A few random thoughts;
If you're planning on keping this trailer for some time, and there's a high likelyhood that the fender hasn't seen its last impact with a guardrail, I'd do what you said, and just pound it back in to some semblence of shape, and go on with life.
On the occasionds when my wife has made this sort of "ooops", I've found that quick and complete repairing of the mistake usually causes her to forget it long before I do. A little bend or two in the fender might serve as a constant reminder.
The general contractor I work for has several trailers. I have a couple of my own. Generally, when someone has raked one against something, it was because the tow vehicle didn't have adaquate mirrors. (Not to say that's ALWAYS the case) Maybe your wife can shed some light on that aspect.
Some people just aren't intended to pull trailers. (I have a real problem with the "30 day wonders" CDL/truck driver/steering wheel holder schools.) I've always been of the opinion that if someone has to teach you how to handle a truck/trailer, you don't need to be in one. (One more advantage of growing up on a farm)