Using a combination of Quic Black shampoo and Quic Sheen polish should greatly improve her appearance in time for the fair. Start by getting her thoroughly wet, then apply Quic Black full strength to a sponge, and scrub into the areas that are supposed to be black. Don't worry if you get some on the white areas, in normal usage it won't stain. Let the Quic Black stay on the hair for 10-15 minutes, then rinse thoroughly. For a brighter contrast, use Quic Silver on the white parts at least once before your show, following the same directions

Scrape, towel, and/or tie her in the sun until she's damp but no longer soaking wet. Then spray the whole body with Quic Sheen. Quic Sheen provides moisture, makes the hair repel dust, and further enhances all coat colors. After applying, keep her confined so she does not roll until she's fully dry.

Given your short time frame, I would suggest two treatments for color enhancement--one ASAP, the second as close to show time as practical. Lots of rubbing in the interim will help to bring up natural oils and give her a healthy glow.