I have a 7 year old collie/lab x that I have had for 3 years from rescue. When I first got her she was excitable and friendly to ANY other dog and would run over and be friendly and playful. After having her about 6 months, she was attacked by an old female bitch twice and since this time her aggression to other dogs especially females is bad. When she sees another dog across the park she barks and runs towards it, heckles up. If the dog is male, she is very playful, taps its head with her nose, runs around and is very very flirty. However, if the dog is female she barks aggressively and a couple of times has had got into full scale fights which im sure has reinforced her hatred of other female. I have to get her back on the lead whenever another dog is around incase it is female and sometimes im not quick enough. Im loathe to muzzle her, but should I? She is spayed. My husband plays with her very aggressively which she loves and knows boundaries/ limits of aggression towards humans, but i worry this aggressive play also reinforces that its ok for her to act this way. Please help? In every other way she is a loving placid character but I don't wish to be an irresponsible owner, or prevent her socialising with other dogs which she loves- but only if they are male!