The 51% owner occupancy law and who pays HOA dues when a condo is foreclosed on?

I currently own a condo in a building of 4 units/condos in Denver Colorado. I rent out my condo and so does my neighbor upstairs. One of our downstair neighbors has been trying to sell her condo for several months now. She had an interested buyer recently but was disheartened to find out that the building must be 51% owner occupied to be able to sell her condo (We all used to live in our condos but life changes forced some of us to rent them out). Therefore she is being forced into foreclosure as she can no longer afford the property and she now lives in Atlanta, Georgia and she does not want the hassle of trying to manage a property she is not around. Our question is, as the HOA and owners of condos in the building, how does a foreclosure affect our properties? And once the bank takes possession of the neighbor's condo who is then responsible for paying the HOA dues? How can this ludicrous FHA rule of 51% owner occupancy apply to a building with only 4 units (which would mean 3 units must be occupied by the owner)? And how is one expected to control what another owner is going to do with their unit? (i.e. rent out their unit).