My daughter was a flowergirl at just turned 4, with a gorgeous dress made for her. That dress attended a lot of parties (especially but not only those with a "princess" or "fairy" theme) over the next few years. The dress you link to would look like a play-dress in comparison, so absolutely go for it, looks a lovely party outfit.
(come to think of it, the last outing "the dress" got, I think, was as a costume in a school play for her younger brother when he was 7...)