3 year old spayed female behaviour change

I have a 3 year old female who is spayed and is just about the friendliest dog in the planet to people and other dogs as she's been well socialized all her life and is generally very submissive to most dogs, with the occasional one she just wants to ignore.

She's only been on 1 sorta of fight and that was with one of her good friends over a ball in the park and they both got carried away but no damage at all to either dogs so as with Staffies its usually sounds worse than it is.

But one change I have noticed is that randomly when walking her on lease in and around the neighbourhood she will sometimes see another dog.. usually smaller dogs and start growling, hair up, power stance and start pulling towards them. Now half the time we are close enough that she's got close to the dog and then its all happy time and tail wags and sniffing. The other half of the time it instigates the other dog and then its break apart time and calm down.

I am not worried she would hurt another dog but this attitude of "tough dog making a a big show and noise" is new and can make people think she's aggressive or dangerous.

Has anyone had a similar situation and any advise on best way to treat these situations? I make sure she doesn't fixate or stare at another dog as much as possible but I also don't think pulling her back on leash is the best solution either as I am pretty sure that makes it worse.

Any thoughts would be much appreciated as I know there's no perfect dog but a year ago she greeted every dog with the same goofy, super friendly demeanour and now.. well maybe now its just that she's getting out of puppy stage and has an issue with certain small dogs when on leash.. but I am hoping I can train myself and help her learn why she shouldn't get like that.

Big love to the Staffie families from Vancouver, BC.

Aren