Not saying it can't be done but let's do a little reverse math. Part of the problem is we don't know the trucks cab configuration and payload so let's use worse case scenario.
-A Crewmax Tundra has a payload around 1300lbs (yes, low, I know)
-A 2 horse trailer will weigh 5000lbs+ with horses in it. Those trailers are fairly balanced but you're probably looking at minimum 10% on the tongue (500lbs)
- A lady that rides horses is probably fairly light ;) so call it 120lbs
That leaves us with 680lbs of payload left for a loaded TC. And that's assuming they travel alone.
1300-500-120
Even 1 person will pack at least 200lbs of stuff for a weekend including clothes, food, dishes and utensils, cutlery, beer....
Now down to 480lbs of payload left for a TC. I have never seen one that light. That'd be a tent on a sheet of ply in the bed.
The more popular double cab Tundra buys you another ~200lbs of payload. Still doesn't leave much for a TC. A rare regular cab 2X4 work truck gets up to 2000lbs of payload but I'd be surprised if that's what she has.