That dress would look great with a classic strand of pearls. For a twist, you could do a two or three strands together with a multi-strand, silver, antique-style spacer to help them lie flat. The earrings could be drops on hook earwires with the pearls on a straight pin accented by bead caps.
I realize that was a lot of bead crafting jargon above, but your sister the beader will know what the terms are.