Joe is right. She gets in a wreck, and not only her, but now you, are potentially libel.
I was involved in a wreck a few years back. Luckily I had $500,000 in coverage.
5 cars involved, 4 drivers, and the owner of a car driven by one of the people involved were sued.
If you loan your vehicle, or in this case, your trailer, you assume the risk.
Talk with your insurance provider and see what they tell you.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.