In Victorian times, a skull was not an unusual thing to have in the house. Be it on the side board or even on the table. It was considered to be a reminder as to our fallibility and an inevitable end to our earthly existence.
There is a famous Mexican painting/drawing of two women at a cafe, wearing hats. On closer inspection the image is entirely of a "skull". I found it clever and have never seen anything to match it.
I don't know why she freaks out at skulls for we all have them, it's just ours are currently filled in with skin and cartilage.
There were some supposed "embedded" images in some WT magazines a few years back maybe she thinks they are some sort of demonic thing. Strange thinking, considering if she didn't have one her face would not exist.