My Dog around others?

I rescued my dog a year ago now and last few months she has been funny around other dogs if there is one behind a fence barking she will pull like anything to get away this morning i took her for her booster jab and its 1st time taken her to vet since had her and she played up something rotten as soon as another dog came in she was barking yelping whinging pulling quite bad it was quite embarrassing lol also have had a friend over before with her dog and she was ame with him and i think probably putting him in his place in her home we are wanting to rescue another dog but quite worried about doing so with her like this and any reasons why she is like this now when she didnt used to be