Before the board descends on this person in full perhaps additional constructive suggestions of what to ask of UA would be helpful.
Requesting a refund for the bag fee would seem to be top of the list. If contacting UA customer service is yielding no results sending a letter to your state's consumer protection agency may yield some results. I would keep things simple and leave the issues about seating out of the letter.
1. One bag was overweight. One bag was underweight.
2. The agent refused to allow the passenger to transfer items from one bag to another to comply with the weight limit.
3. A baggage fee was incurred which should be refunded.
I'm not sure what can be done at this point in time about the separated seating. It's happened to us all unfortunately. Asking for some goodwill credit in writing (postal mail) may work. But getting a "full refund" isn't likely to happen since you were transported after all.