There are a couple of ladies sitting on the right and left top corners of the mausoleum These do not appear to be angels. This lady is clearly a musician playing an instrument of the Gods, a lyre. Here is link to a discussion of lyres as mausoleum art. I gather this statue symbolizes a harmonious spiritual connection with God.
I was curious about the bare nipple but when I googled it I was directed to some "dangerous sites." I'm sure the bare nipple signifies something but I'm not sure what and may never know. The meaning is hidden even if the nipple isn't.