Confusing tombstone in my sim's inventory

I have a cute little hood where I play my own sim families in Newcrest.   I play on a long life span and none of my sims ages - not yet anyway.  So far they have all completed their Soul's Journey and now I am working on their aspirations along with trying to break the record for how much nectar a sim can make (only kidding on that one) though I love nectar making.

So I finally got to the last sim's house in this rotation and just as I loaded her house I got a notice that she had completed her aspiration.  Nice, but she could have waited for me.  She is a spellcaster so it isn't that hard really especially as I love the role and have a few spellcasters in my save.  However, that is not what puzzled me.  What was strange though was a tombstone with her name on it sitting in her inventory.

Now, she is very much alive but this was a proper spellcasters tombstone with the little jewel on it. It was a little disconcerting to see it and I have been wracking my brain ever since trying to figure it out.  Did she somehow die while I was away playing another family and some kind soul resurrected her?  Why would she pick up her own tombstone though?  That is not something I would expect a sim to think of.  Maybe it was a mean prank but do these things happen when you are not playing a house?  It was prank day fairly recently.

The tombstone seems to work as it should too.  It changes to an urn if I put it inside and then back to a gravestone if I put it back in her inventory or outside.  I have even strengthened the spirit's connection just to see if anything happened.  It didn't.  I guess I could put it outside and hope her ghost appears.  I didn't think of that.  Will have to go back and try it.

The only possible clue I can think of is the last time I played her house I got her to cast Duplicato on herself.  I have never cast that spell before and, to be honest, it seems pretty pointless.  It creates a clone of your sim but with a different name.  Her name is Jasmine but I think her clone's was Isabella.  Isabella did not do anything much.  I had no control over  her. She hung around for a day or so and then disappeared off the lot and I assumed she was deleted from the game.  Maybe the tombstone was her's despite her having a different name or maybe just having her in the game caused it.  I can't remember how many days I played her house after Isabella left though I think it was a few.  Probably just a red herring anyway.

Anyway, if someone could think of a better idea or explanation  I would be most grateful as it is bugging me trying to come up with anything other than a glitch in the game.  I have searched online but haven't found anything recent that could explain it.