Is there an easement on a neighbor's property to maintain a residence built to the property line?

My friend tore off an old "lean-to" from her house. Because there was an existing slab, a zoning variance was granted to build a new addition even though it aed the property line. This completely upset the neighbor. After construction started, the neighbor posted a no tresping sign. Now construction has stopped and water is coming in. Can my friend step on the neighbor's property to side the wall?