If correct, this must mean that Princess Maud (or possibly her mother) had access to the tiara before the death of Queen Alexandra.

I am not sure I can agree that Princess Maud is wearing the emerald necklace in your photo. As RDavid says the necklace greatly resembles the sapphire necklace that we know for certain that Princess Maud did own. The stones in this necklace look very round to me, whereas the emeralds in Queen Victoria's necklace appear as rectangles and importantly, between each large emerald is a smaller emerald, there appears to be no darker smaller stones breaking up the the larger darker stones in Princess Maud's necklace. I don't think we can say it is purely a trick of the light as Princess Maud is wearing a small dark stone ring which shows up well.

I hope these pictures illustrate what I mean.