Legal Question in Real Estate Law in California

I would say that California case law, as well as a careful legal analysis of CC 1008's wording, supports the view that permission granted under a CC 1008 posting is revocable by the owner and that permissive users do not develop any lasting rights as a result of the CC 1008 posting having been in place. The signs would, in effect, create a license for use of the road, and licenses are generally revocable. I would hasten to add that there is a slight chance that your new neighbor can assert some right to use your road under some other theory, having nothing to do with CC 1008 or your signs. She might be a successor in interest to someone who obtained an easement by prescription years ago, or she might have easement rights under another theory, e.g. easement by necessity, or an easement by implication, a/k/a implied easement. Therefore, I cannot say with certainty that you can lawfully lock her out. I think a better approach is to try to learn what theory, if any, she can give for her right to use your road.