I agree with Arthur; it certainly looks like the fringe brooch on both occasions.
This shows how the fringe appears to my eyes and as Arthur described:
Perhaps I am misreading the comments, but no fringe can be seen on the 1950 photo because the program is covering it. But even if it was not obscured it may not have been visible anyway. Look at this photo below on the left of HM in France earlier this year. The fringe is nearly lost in the pattern of the dress. When the photo is changed to a low quality black-and-white image as we have of the Queen Mother then the fringe is even less visible and would be much more difficult to detect if the dress had been covered with sequins.