Bad doggy

Two items of Lucy news:

1. Lucy had a lot of fun while I was at work on Thursday. The door to the closet with the doggy treats was left at least a little open, I guess, and Lucy managed to pull out the box of Greenies, remove the lid, tear open the resealable pouch they're stored in, and eat probably five of them. I came home to green doggy puke around the living room. Very gross. I have evidential photos, but Picasa won't let me share them. Perhaps that's for the best.

More importantly,
2. Lucy has become aggressive towards other dogs. I started to notice this right after we moved here. She growls at other dogs we walk by when we're out, and if I give her enough leash to go say hi, she picks a fight. Some of the other dogs are the same way, but plenty are afraid, and I feel so bad. I let her play with another dog, a big golden retriever, in the park the other day and just droppped her leash so she could approach on her own terms. They were fine. So I took her to the dog park again today thinking maybe she just needed to be off-leash. We only stayed a few minutes because she wouldn't calm down. All the dog rushed her, of course, when we went through the gate. I saw her hair go up and she sort of snipped at some of the other dogs. I thought she would chill out after she ran around some, but she wouldn't. I tried to talk to the other dog owners about it while I sat with her, letting the other dogs approach me so I could pet them and show Lucy it was okay. I tried to tell them she had been completely social and very outgoing pup until a month ago, but one just told me that it was "not normal social behavior" and seemed to intimate that we should go. So we did. My heart literally fell when we walked out of the dog park. What happened to my nice doggy? Wes and I have always talked about getting another dogon day, but now what? And it's pretty hard to keep her away from other dogs in the city. I feel like the parent of the kid who misbehaves on the playground, except here I don't know how to handle the situation except to keep her away. Suggestions, anyone?