Title

Drive over to the Virginia DMV, with the title, and ask for a supervisor. That is where you will get definitive answers.

Apparently you never licensed the trailer after you bought it. You should be able to take the title you have to the DMV office, fill out the paperwork, pay the fees and get a new title. There should be no need to get California involved.

If you have a bill of sale that would help. Actually she was suppose to send release of liability to CA DMV and you re register within ten days. Don't contact CA DMV if at all possible. Like most government agencies, few if any employees really know what they are doing.

westernrvpo's answer is great.

I've sold vehicles/toys without having transferred the title to my name.
Signed title is a signed title in my experience and I've also been able to title vehicles I bought that were not titled in the sellers name.

Each state may vary and it may be an uncomfortable conversation for you with the buyer, so you can either title it in your name first and they can winder why you just titled it last week, or you can explain you never titled it.
Nothing to worry about IMO.

If all else fails, Virginia has an option for abandoned trailers and vehicles.
abandoned vehicle

The process is described.

If you are now a Virginian, start with the Virginia DMV.