I'd find a deserted straight road, or a large empty parking lot (lot's of those at schools and malls around here) and give it a good test. If they lock up again get out and see how many locked up. If it's only one then you could have a mechanical issue where a broken spring or star wheel adjuster is wedging between the shoe and drum. If all four are locking up adjust the controller down. If you can't replicate it then I wouldn't be too concerned.
If I had my DW follow me I'd be scared to death that she would be preoccupied with watching the trailer wheels that she would end up rear ending the trailer.
I do love her dearly but she's a terrible driver!