The two pictures are similar, but some of the jewels are different. Here we have two different pairs of elaborate earrings, a more elaborate pendant in one picture, and also the diamond cross. If the engraving is really a record of the jewels given by George III to his bride, I think we may be seeing an early example of the transition from stomacher as cloth insert to stomacher as ornate diamond bodice ornament. Queen Charlotte had the possibility of both.
I have been thinking about the silver bodice front which looks like silver lace in some pictures and more like diamonds in the state painting with the unidentified crown. I wonder whether anyone has asked the Royal Collection if part of that stomacher still exists.
As for the crown, I have enlarged it as much as possible and then used a magnifying glass. It seems to me that the basic structure of the Mary of Modena crown is there, supplemented with metal crosses and many gracefully arranged diamonds. The presence of scepter and rod behind it, and Queen Charlotte's hand touching it, as well as her state robes and youth, suggest to me that this is her coronation crown, probably realistically painted. The chair or throne even has her CR cypher on it. All very majestic.
The description of the Mary of Modena crown says that its frame is copper. Since it was a century and a half old by the time of Queen Adelaide's coronation, the condition of the frame could have been a good reason for her to have a new crown made. Or perhaps she preferred a finer metal.
Edit: I have always understood that Queen Charlotte wore the Mary of Modena crown. The article linked below says that she had her coronation crown made. But she was crowned with her husband only two weeks after their wedding day (the day it says they first met), so I wonder. There is also an indistinct picture of their wedding on this page, but one can make out the tiny crown. The picture said to be Charlotte's coronation portrait is very similar to the one we have been looking at, and matches her husband's, but she has quite different hair!