Bonnie is now day 15 of her 1st season. I believe that it continues for about 21 days? Is she then safe to go back to normal off-lead walking? If she is still discharging at 21 days should she still be on a lead or is it safe to mix??

21 days is the average length of season in the average bitch. After this time her vulva should have shrunk back down again - although it won't ever be as small as puppyhood - and all discharge stopped. This is when you can give her a good wash and wash all her bedding to remove any lingering traces of her 'perfume'! Take care when allowing her back into canine society again because some bitches take a few days more than average. :)

Thanks Jeangenie, very helpful. It's day 19 now and she seems to have virtually stopped discharging. I'm looking forward to being able to let her have some off lead fun later next week!