behaviour advice needed please

Hey all. Hope you guys can help me with advice as you have all been helpful in the past.

Poppy turned 2 a few months back....she has never had an issue with other dogs. (Well apart from wanting to play with every one she saw

However over the last couple of months she has totally changed. Apart from the dogs she knows she now seems to dislike all others. If out on a walk and she sees one the hackles go up and she tries to pull on her lead towards them. Occasionally she will quietly growl as well. I honestly don't know where this behaviour stems from but I find it really concerning. (She is kept on areas at all times obviously)

Tonight has just tipped me over the edge.....I let her out for a pee in the garden. Luckily I was stood at the door as two people walked past quite innocently with two dogs on leads. Poppy ran up to gate barking away,hackles up, and was actually trying her best to jump the fence. Luckily it was icy so she couldn't get her grip. She has never done this before. Literally at my wits end. In all other aspects she's a great dog but this behaviour worries and upsets me. Help please. Thanks x

Has poppy mixed much with other dogs?If you have a friend/family that own a really dog friendly dog try lead walking them together with you and the other person in the middle and the dogs either side,try this a few times until Poppy is ok with it,then try putting the dogs together(still on their leads)and walk together until Poppy is happy being close to the other dog,hope it helps

read this link also,it should help
http://staffy-bull-terrier.com/dog_body_language