It is normal that when dogs meet there would be a certain amount of posturing or growling, if she doesn’t do it too often there is nothing to worry about. What you did was great, but once you get them on leash to control them you must not forget one thing; for most people its natural to hold the leash high and tight. This will pull the dog's head up, making him look aggressive and in a position ready to fight. try to keep the leash low so they can say hi to each other without giving the wrong impression.
Another thing is, never punish her for growling because that will make her hide it and will give you less opportunity to know what’s going on. She would make a negative association with the new dog. Praise her instead when new dogs are around, give her a treat to refocus her attention on you and that way she would be really happy when other dogs come around, she would be thinking hey! Time for goodies!