Legal Question in Real Estate Law in California

As you said, she has the right to cut down any ranches hanging over into your yard as long as doing so does not endanger the health of the entire tree. You are responsible for repairing any part of the fence that the tree has damaged. How yo will do that without going onto her property is unclear.

The previous answer is a bit unclear. Actually, if the trees are growing on your property, as measured by where their trunks stand, but branches or roots intrude onto the neighbor's property, the neighbor's remedy is to cut them or have them cut at her own expense at the property line, which she may do without a court judgment or order. However, she must do so in a way that does not result in permanent injury to the trees nor create a safety hazard, e.g., that the trees may die or topple in a windstorm (like we're having now).

If the trees are growing on your property (as determined by the location of the trunks) or are growing on the boundary, she cannot cut them down.

Further, if the problem is truly only a few loose and displaced boards, maybe the solution, at least in the short run, is temporary repairs, which could be quite cheap, I'd think.

Neighbor problems of this general kind are usually better handled by diplomacy and negotiation rather than by arguing back and forth over the fine points of tree-and-fence law.