Common wall hell in CA

[AVM1]

I live in California, and I have a "patio home" built in the late 1960's. It's a one-story home, and I share an interior wall with my neighbor. Outside of the house, in my front courtyard, is my neighbor's exterior garage wall. The entire length of the garage wall is in our front yard area and basically acts as a common wall. The neighbor cannot see this exterior wall from her home, but we do as it's literally in our front yard area. I consider it a common wall because there is no easement, space, or fence separating it from our property line. This is typical of most patio, or semi-detached homes. the problem is that we are selling our home, and wanted to make the ugly block wall more attractive, so we nailed two 4' X 8' white lattice panels to the wall. They are not permanent, nor "anchored" into the wall. It is just some garden art to make the wall and area more attractive temporarily. Well, our neighbor blew a fuse over this and insists we are encroaching on her wall, and her property rights. But what are OUR rights? This neighbor could put 10 inch metal spikes into this garage wall, and we'd have to look at it? Our HOA is of no help. They are being intimidated by this very obnoxious, crazed neighbor. We brought this situation before them, and they initially sided with us and gave us written, official permission to place the lattice panels on the wall. Today, we received a letter from them telling us our request has been denied! I think the problem is the nature of the home itself. There are no city ordinances that address these types of homes, as they are not really condos or townhomes, and the HOA is probably afraid of a lawsuit so it is giving into the screaming neighbor. Isn't there something in the law that allows for "reasonable expectations"? that is, if you purchase a home that shares interior walls, and has an exterior wall right on the property line, isn't it reasonable to expect that you will have to share it in some way, and cooperate with your neighbor? If living in such close proximity upsets someone so much, perhaps they should have bought a traditional, free-standing, single family home instead. Any help or advice you could give us would be very much appreciated. Thanks in advance.