Because we are examining sketches and possibly watercolours, which were never intended to be a precise reproduction of the jewels, it is difficult to say with certainty; however, after looking at how jewels were depicted in other cards in the series, it is certainly possible, in my opinion, that the tiaras worn by Queen Victoria and Princess Christian are the same as that worn by Princess Marie Louise.
Below are some from the same series. What interests me is that, although I can recognise the tiaras, they are not precisely drawn.
I am still intrigued, however, by the various reports which say that the tiara had large or "fat" turquoises. Below is another report from the 1911 exhibition. I wouldn't describe the stones in any of the depictions as large.