Very strange speech problem

Very strange speech problem

My daughter has mosaic down syndrome and triple x syndrome.  The combination is so rare that there might be only 20 people in the entire world with both, therefore I do not have a lot to go on.  My daughter started speaking early at 10 months.  She clearly said, "I'm Up", bob for dogs, mum, dad, and book.  One day they were all gone.  She is in speech therapy and is doing the same thing.  She will say bubble for a long time and then it is gone.  Some words have resurfaced like bob but now it is not only for the dogs, I am also Bob and so is my husband.  Has anyone heard of a child speaking clearly and then losing the words?