7 Month old shows aggression while on walks and leash

[Scout33]

I have a 7 month old German Shepherd, that I got from Animal Control, when she was about 3 1/2 months old. She was very skittish, barked alot and did not like others coming to our home. I've worked with her and she's done a ton better. I had a party a couple weeks ago at my house and she was allowed to bark when the guests got to the door, but was told "enough" and would stop and was very good with each guest. I take her to doggy daycare twice a week and she does very good there and we go to off leash dog parks a few times each month. At dog parks she barks and runs up to other dogs (she's not interested much in the people), which can be pretty intimidating to both the dog and their owner, but if the other dog comes at her or chases her, she comes running towards me with her tail tucked. What scared me the other day was while I was walking her on her leash. We were at a park and I noticed a guy that I use to work with and his wife with their dogs. I said hi and he started to walk towards me, she was going crazy. She wanted to go over to his dogs (that his wife was holding at bay), but she really did not like him talking to me. I could not calm her down and she lunged at him a couple times. Needless to say it wasn't a good visit. I'm just wondering what to do with her aggression, it seems to be really bad when she's on a leash. Has anyone had a similar situation and what do you do about it. Thanks.