She cleaned up nicely using "Chemtech CT18 Superwash". I diluted it around 10:1, sprayed it on, let it sit for a while and hosed it off. Most of the road grime on the engine and brake dust on the rims came straight off, while some of the toughest bits needed a light brush and then came off easily with a second rinse.
Chemtech CT18 Superwash is available from Repco.