Just my 2 cents on that... You can not be sighted for US DOT regulations, if you are "not" USDOT certified (driver's log book, inspection report, fire extinguisher, DOT #s and so on). IMHO, 3/4 or 2/3 of those tickets should have been throw out right from the start.
The other tickets on weight class/not being DOT/CDL... Just because the "trailer" weight rating put her over the 26,001 when connected to her truck doesn't matter, its the truck's weight class and if that combo goes into a state weigh station and comes out to 25,999 she is ok not to have a CDL... BUT, yes ALL truck/trailer combos (well ok we have the RV exempt that don't need the numbers) have to be USDOT when over 10,001... 2 USDOT classes are for the little guy (me for example), 1, "Pvt not for hire" and 2,"Exempt for hire"... IMHO that is the "only" ticket she should have received, not having a US DOT #.
I use "Exempt for hire" with this combo to transport horses for pay... 06 F350 (23,500lb rated) and a 6 horse head to head trailer (16,000 rated)... I have driven many states, DOT stations, Ag stations and not once have I had any problem. Maybe because... I have 1 of many rules, I will not travel west of the Mississippi. Some how the rules change from legal the farther west and it would be MY job to correct the officers of their mistaking of those laws, no thanks.
A bit off subject of this thread? Maybe, because the combo talked about here, will need to be usdot numbered, UNLESS wanting to take the RV (LQ) of the trailer into the subject... But there you go, what trooper is going to say "ok no DOT needed" and what trooper is going say "yes you do need DOT#"