Since you already know that your ex may not avail in court, you may choose to inform the police immediately. However, you need to have clear reasons why you think she will not attend the court. You can as well go to the courthouse where the bail was settled and tell the justice who was involved to counsel the bail. To read more login http://www.heyenslaw.ca/bail_12.html
You can't revoke it. The police can't do anything until she actually misses court, at which point the court will issue a warrant for FTA (failure to appear). Oh, and when that happens you're out your $500. Did you pay the police or a bondsman?