Tango's dog aggression

So, when we first got Tango and Schroder home from the rescue they were great- Tango was running around with other dogs, and when we went on walks she would sniff other dogs we met but didn't seem to really notice either way that they were there.

I'm not sure what's going on- if i'm just being a wimp or something and causing the problem- but she's starting to get dog-agressive. We meet other dogs on our walk, and largely they are very polite- they come up slowly, sniff noses, slowly edge closer together to smell each other's butts. Schroder is all oblivion and wagging-tail, and then Tango leaps at the other dog snarling.

Tango is very aware of other dogs- it's like she's spotted a cat and goes perky-eared, her tail goes up, and she freezes. The other dog approaches (with permission from the owner), and Tango appears to relax and do the whole sniffing thing, and then she lunges out of the blue.

When she gets hyper-aware, I redirect her attention- treats, pets, getting her to sit or lay down, whatever. When she's calm, I'll let her sniff the other dog. First sign of intensity, we go back to sit- look at me- treat. She keeps breaking away from me to leap at them, though, or will do so during the sniffing process (I'm watching for signs of intensity like head higher or lower than normal, ears further forward, tail too far up or that weird "I'll pretend to like you" wag, but it keeps catching me by surprise when she goes for the other dog).

At first I thought it was a "lets play" sort of leap, but the other dog always backs away like they're scared and then is very careful to keep distance from her from then on- so obviously not playful.

Whats up with this? What should I do with her?

sounds like she is coming with leash aggression. Do not let strange dogs come up to her on leash. They have a fight or flight drive, and when on leash most dogs fight because they can not flight.

Simple as that, eh? It's just odd because it's appearing out of nowhere, and as far as I know nothing has happened to her when she's on-leash so I don't know why she's suddenly freaking out about it.

She also did the same thing once when off-leash - but, I didn't mention it because the other dog was leaping all over her and barking like a mad fool. I am not a fan of little dogs for that exact reason, so I don't blame her at all for getting aggressive there.

Now that I know it's that simple to resolve, everything should be OK now. Hopefully.

I never said it was going to be easy. This is where you are going to have to sturdy your ob with her. Teach the look at me/ or focus command. It will take a lot of hard work.
It is easy enough that it does not become a fight, but never easy to correct

Nothing with her is particularly easy- she is smart, stubborn, and has a one track mind in regards to EVERYTHING. However, she's very motivated by food and lovin' so that's helpful.

So far getting her to focus on me mostly works, unless the other dog is particularly interested. I just wanted to make sure I wasn't screwing anything up and somehow making her increasingly aggressive. I don't think I am, and I'm careful to always project a feeling of calm, secure, and in control (particularly when I get nervous about something).

If I can work her down to the point where doesn't think that another dog approaching HAS to end in a flight/fight response that would be good, but I can see that taking a LOT of work to accomplish. We'll work for now on just not attacking other dogs when they approach (a lot of people around here go for off-leash walks, so it can be hard to avoid interaction)