When I trained dogs in town I got up real early and walked them to avoid other dogs, if I couldn't do that I would drive to the outskirts and walk them. Maybe find or befriend other trainers that have a straight track or big runs that wouldn't mind you using them a couple times a week and even slip them a few $ or a bag of kibble now and then so you don't wear out your welcome! If the mongrel is a serial offender call the pound! I have never used one, but some swear by walking machines. Don't worry I still got menaced many times by circling @!#$bag mongrels that came out of nowhere!
I hope the bitch recovers and all the best with her racing career!