There are a few blue flowers to choose from, was the purple one Lisianthus? Its fairly common for weddings and such. A good blue one is Eryngium 'Jackpot', it has a really good blue color and a slight metalic sheen so it could really fit in with the silver too....it all depends on what her tastes are. It would look fantastic with some softer flowers like 'Heiress' or even 'Vendela' roses! 'Heiress' is very soft and elegant and fragrant too!
There is also Gentians, they are a real true blue but more closer to sky blue then navy.
