How to socialize a dog showing increasingly aggressive behavior?

I have a three year old American Bulldog that has become alarmingly aggressive to strange dogs.

She is sweet to my other two dogs and to all people.

But she almost just killed a dog a little while ago.

I was taking her running on a leash, a neighbrs dog got loose without a leash. I normally can keep her away from loose dogs but this dog made a beeline right at her face.

As soon as the dog (which was a chihuahua) was inside her personal space she snapped at her and had the whole dog in her mouth pretty much. I had to put her in a headlock and open her jaws to get the little dog free.

She never used to be like this until about a year ago when my next door neighbor got a dog that would bark at her through the fence. She has developed a severe desire to wtfpwn any dog outside of our yard.

I used to bring her to dog park and she was fine.

Should I just put a muzzle on her when she runs?

I have to take her running...she has to have the exercise.