What someone else posted is true: white chocolate is not truly chocolate because it lacks chocolate liquor/cocoa butter, but there are many things you can purchase (including at your everyday grocery store) that are used both as dipping chocolate or in chocolate molds. When I refer to white chocolate below, please keep in mind that it is not true chocolate.
1) Bakers brand makes a white chocolate for baking, sold in the baker aisles at grocery stores. This chocolate is a little bit more sensitive to warmth than other options, so it may not be the best bet for molds.
2) Most grocery stores carry something called chocolate bark or confectioner's chocolate, sold in bricks (often in the produce section) in both milk and white chocolate varieties. This type has a firmer/drier texture than the baking chocolate mentioned above, and usually works well for both dipping and molding.
3) Wilton Candy Melts (and other brands of candy disks used for making candy) work very well for both dipping and molding. These come in dark and light chocolate (actually have a cocoa butter content, so they are "real" chocolate), and various colors and white (these do not have cocoa butter.) If you put these in a plastic disposable cake decorating bag (or in a plastic freezer bag), then melt the disks in the microwave, you can snip of the end (or corner) of the bag to easily squeeze the chocolate into your molds or drizzle zigzigs or other accents onto already formed chocolates. (Note: Wilton also sells special candy colorings for tinting the Candy Melts, as well as candy flavorings. You'll also find other candy flavoring options in stores that sell candy making tools.)
If this lady who was hired to make these chocolates (is she making the wedding cake?) doesn't know about these options, she is not an expert (in my opinion). Perhaps she is a cake baker/decorator and doesn't usually do candies, but as a cake decorating teacher and decorator for a catering company, this is product info I would consider to be widely available and would expect someone working in the industry (cakes, candies) to know. Even if she is not using molds and is forming these by hand or by cutting them to shape, these white chocolate products are widely available and would work in some way as outlined below.
White (or other colors) of the melted Candy Melts can be squeezed (as described above) or painted into parts of the candy molds, allowed to set, then filled in with other melted Candy Melts (or other chocolate, white or regular) to fill them up. Chill the molds then pop them out. Alternatively, you could mold the candies in whatever color/chocolate, pop them out of the molds, then paint or pipe the details on top in the preferred colors.
Of these options, I'd say Candy Melts are the easiest to use. They can be purchased at craft stores such as Michaels (Hobby Lobby stores sell another brand, I think it is Make N Mold) and some SuperWalmart stores stock them in their Cake Decorating section (part of the craft/fabric area). You/your sister could probably locate some of the shapes (airplanes, etc.) as candy molds online and attempt these at home yourself. (Included in Sources are links to the Wilton website, plus a link to options for airplane molds at Ebay and Sugarcraft, a company that sells cake and candy supplies. You'll find other options searching "Airplane candy molds" on Yahoo or your preferred search engine.) It might take a few trial runs to get the appearance/quality up to par, but at least you'd get what you wanted. Or simply tell this lady about these options.