Aggression

Hi I am sure this problem has been talked about before. Its regarding a Patterdale that came from a rescue after being dumped.She is a lovely dog but seems to not know when to stop. She will attack other dogs and even when they are completely submissive laying on their backs crying she does not stop. It makes no difference on size of dog, cats as well...
She has been out of the rescue about 5 months
She is now muzzled when out and sometimes when inside if in a place with dogs or cats.

I have taken her on walks with my dog and we go where there are lots of fields smells etc...I do not muzzle her and it is no problem we have even come accoss other dogs where i put her on lead and encourage greetings followed by lots of praise and so far so good.
The owner is about ready to give up on her and send her back to rescue..and has asked if i would like her....I have a small dog who is