Fear aggressive

My bitch has just turned 3 she's always been a shy dog very submissive and would run away from strange dogs. But just in this last month she changed she's standing her ground all her hackles up. If the strange dog comes near she snarls and growls. She fine with my other dogs and friends dogs. She's a spaniel gsd lab cross. My other dogs are all friendly with other dogs and don't even react when a dog goes for them. How can I help her I need to put this right.

I hope other posters can offer suggestions. All I can do is offer sympathy. My Sophie has always been a complete fraidy dog. We adopted her as an adult and whatever in her background made for a very timid dog. For a few years there she did better. I could take her for off lead hikes and even to the local dog park.
Very shy with strangers and dogs her size or bigger. But little dogs were her best buddies. She'd lower her chest to the ground so she could play nose to nose. I wish I had a video of her with all these toy dogs in pretend chase.
Then a few years back she started to go weird. Two different men and she went bananas barking at them.

Then the corker was when she attacked a puppy and a grown dog both completely unprovoked. But now she is a senior, I always keep her securely on leash, well away from other dogs.
Your pup is young enough that you can turn such behavior around I'm sure.

She's got the size of a small lab and looks like a lab but a lot of her traits are gsd. Which causes some problems. She's been socialised well and came to work with me full time when she was little I work in Leeds. It seems to be dogs her size or larger that bring it out of her. She took on a rottie the other day which was scary to say the least. She was attacked by a unknown big bull breed about a year ago and she just lay down till we finally got it off could it be that ? It was ages ago .

Hi Joanne you could try desensitisation, going somewhere where other dogs can be viewed at a safe distance and rewarding your girl for ignoring them.

You need to find somewhere frequented by dogs on leads and go armed with a good supply of tasty treats and a toy then sit/stand at a safe distance ignoring the dogs completely then play with/talk to your dog and 'treat' when she ignores the other dogs. It takes a lot of time and consistency for it to work.

Chloe is dog aggressive having been bitten by two off lead dogs (one my neighbour's dog) , I live with it doesn't really bother me because I live right out in the countryside and can go where I rarely meet other dogs.

She's fine if she's on lead and they are. It's when they want to actually sniff her and greet her. She makes all the right moves they suddenly the teeth come out full snarl leaves the others confused. They move away "hopefully" she will then follow them to instigate play when they do she snarls again. My fear is she's going to get what she appears to be asking for.