If the weather is decent they may well be in flower then. You may be able to order these particular blooms from floral specialists. I know my friend had white muscari in her bouquet and that was a special order.

Our blue hydrangeas have always been in flower by then.
Has you daughter seen Blue Moon? it isn't really blue, more a sort of light lilacy colour.

Have you seen Lisianthus, white cup shaped flowers with a deep blue edge, very pretty but best from a florist as tricky to predict

Yes they are lovely - and you can get plain blue ones as well if you want them.

I grew some one year in the gh and got plain white and plain blue, my favorite is the blue edged though and only got a couple of those