Tracking is something in which a less than orthopedically stellar dog can take part.
Here's the link to info on the AKC's site about
tracking. There are RDNs who track their dogs (myself included, tho, alas! Mox has no talent.) and the sport has been discussed on RDN.
Herding can be an expensive activity. Herding lessons cost $95/hour where I train.
Talking to Toggle's foster dad as to her level of gimpiness is a good idea. The biggest piece of advice for a dog with HD is to keep the dog lean.
Play it by ear to see how much activity Toggle can manage and stay painfree.
Swimming is an excellent exercise for a dog with HD. It builds muscle w/o placing strain on the skeleton.
Toggle is a lucky girl to have such a caring owner!