This particular painting does suggest that Queen Victoria is wearing a "high" jewel, but I find it impossible to determine which - except to say that I don't think there are large spaces between the elements which I think would be characteristic of the Regal Circlet elements.
I believe that the series of water colours in the Royal Collection are intended to give an impression of the magnificence of the State Visit, rather than record precise details.
PS I am deliberately using a link to the Royal Collection so that board members can use the zoom feature and read the notes the RC has. I did that also in my earlier post.