While living in AZ. I sold a van that the new owner took to California.
Since plates went with the vehicle, I left them on.

Do not EVER give someone else your plates. Some states require you to
relinquish the tags upon transfer (or expiration, etc). Giving them to
someone else invites just this sort of problem.

I "forgot" to tell her that California
was looking for her for the parking tickets but after getting the title, I
wrote to California and gave them her address and that was the end of
that.

Given the insanity that is Kalifornia I wouldn't be surprised if she had
some recourse against you for failing to inform her of that. grin But
it's good to hear they actually stopped bugging you for it.