There are a number of images of royal ladies (and others) wearing brooches which incorporate an initial and a crown. Some of these were given as mourning jewels and worn by various ladies; others may have represented a gift on the accession of a monarch etc. It is difficult to state definitely what was what without knowing about the period when the brooch was worn.
I hope that someone knows what Queen Alexandra's brooch represents. Somehow I doubt that it was actually a mourning jewel. But!!
Another photo from the same sitting.
Below we can see Queen Alexandra wearing another brooch with the initial E and a crown. I suspect that it was given by her husband, Edward VII after he became King.
In this instance we know that the photo date is circa 1906-7, so it was within the life time of Edward VII.