Help, my pup is attacking other dogs

As some of you may know i've recently rehomed my 2nd Border Collie Toran. She is believed to be around 4-5 mths old when we got her and we've had her now for about a month.
She shows aggresive behaviour towards other dogs that she see's. She doesn't have to beclose to them even if she see's them from a distance she immediatly starts barking and snarling at them.
She has been introducted to my mums 3 Pembroke Corgis and as been getting on great with them untl now. For no reason she keeps trying to attack my mums eldest male dog who thankfully has just ignored her up to now but if he was to turn he would most likely kill her as he is a big corgi!!
I never experienced this behaviour with my first collie Heskey and i'm therefor very unsure on how to tackle this situation and would really appreciate any advice anyone can offer me.

awe sorry to hear this, I dont really have much advice to offer,,,even as a trainer, but im sure one of the collie people will be able to offer some advice,
I take it she is not displaying hearding behaviour due to the snapping and snarling, do you know her history?

Hi we dont know her history only that she was found wandering with her sister who had to have her leg amputated. She was very mal nourished and had a very bad flee investation. We have them as pets and dont use them as working dogs so as far as the hearding goes i dont know. She is the most adorable dog to ppl and to children, its just other dogs that she has a problem with yet she gets on fantastic with my other one!! I just dont understand!!!
I really dont want to have to rehome her else where as i am very attached to her but i really need to get this aggressive behaviour sorted somehow!

awe im sure you will, there are lots of collie owners on the forum who Im sure will have advice on this xx

Do you think she may be ready to have a season, or has she been spayed?

So sorry your having problems, Only advise I can give is go to local dog obedience training school see if they can help.
I hope it gets sorted for you hun.

Our collie has a tendency to growl and snarl if on a lead and bored! she was a farm bred collie, and does not like to stay still.

What is Toran like with other dogs off the lead?

I was going to ask about her season too as it sounds like this has started recently with the corgis???
Has she always been like this with other dogs on lead...and how is she off lead?

Toran is also barking at other dogs when she's off the lead but never attacks them! i put her on the lead and try to chastise her but it doesn't work!

Collies can get very yappy when they are excited...have you tried distracting her from them? Instead of putting her onlead, run in the otehr direction and throw a ball and make YOU uch more interesting???
Where did you get her from? Did they mention dog aggression was an isue?

Totally agree...find yourself a good reputable trainer and they will help you sort it. :smt002