Puppy questions?????

I have a 6 month old Border collie/ australian shepherd pup. Lately she has been very bad and have some questions about this. Is it time to get her spayed and is that one of the reasons she has been bad? Is this just puppy stuff that will pass with training? Have you ever expierienced any of these? Ok so she knows these commands, spin, sit, stay, come, down, off, jump, high five, paw, blow bubble, go get, and bring it. She used to listen to them all the time. Now she will only listens 50% of the time. It's really frustrating. Also another problem I have been having is excessive barking. She will bark at people she knows, barks at people on walks, barks at other dogs. When she barks at people she knows I almost think it's an excited bark but then she will keep backing up until she calms down. Like today she barked at me because I was gone for a day. And her hair stood up. I'm her favorite person too and don't understand why she did it. Also she barks viciouslly at other dogs on walks. Her hair stands up. Should i purchase a spray collar in aiding that? I have been throwing her tennis ball in front of her when she barks on walks but she has not improved. Help? Also she has like 3, 15 min training sessions a day.