[Blagadan]

I found every time I loaned out something like a trailer, I always got it back woth some damage, all be it minor, broken sidelights, cracked fender etc. You loan something out to a person, chances are they are not familiar with using that item, a trailer is a tough thing for some folks to manage when they're not used to it. My brother cannot back up a trailer to save his own life. Always seems to run it into something. I find it costs me less to go out and be the driver. I know this option is not open to you.
Now if your stepdaughter uses this trailer as a tool to cause upset in the family if you DONT lend it to her, then she is not a nice person. I feel sorry for you.
You need to discuss liability prior to loan, if she bends or breaks something, she pays for it this time. Let her know she damaged it the last time and you didnt mind paying to fix it the first time, but if she dings it again, she pays... simple as that...
I find it difficult to say no when my family wants to borrow my stuff. I have no problem saying no to neighbours and friends, preferring to volunteer to help them and make a day of it where possible.
The few times I was lucky enough to borrow something from somebody, I always made it my business to do something to make the item look "good as new" when i return it, be it washing it or fixing it up if something was previously broken on it...