Being protective

I was in the park today and Mia starting to play with a jet x. Everything was fine, they got on really well. Then this couple came along with a Old Enlish Bulldog which was on an extension lead. Mia went over to say hello and just before she got to him they asked if she was a male or female, I said female, ooh they said, he's not good with females. So I went to get Mia's harness to put her on the lead, at the same time this dog went for Mia. I have never seen her act the way she did, sounded like she wanted to tear this dog to pieces. Good job I had hold of her and the other dog was on the lead. They went on their way and when they were out of sight I let Mia off the lead and she just carried on playing with the jet x. I was talking about this toa friend and they said maybe Mia thought the dog was going for me and Mia was being protective. I hadn't thought of this. What do you think ?  

I'm not sure? Daisy is really good with other dogs but if they show any sign of aggression she turns to fight

Darcy is fine of lead but can be a little unpredictable on lead, but if a dog has a go she'll have a go back. Maybe Mia was protecting you.