Puppy And Aggressive Lead Biting

Hello, I have a 15 week old female Aussie. She's wonderful most of the time but she has developed a habit of attacking her lead - she used to do it sometimes in the garden, but now it's only when I take her for walks. The strange thing is that she only does it in two places. The first is on two sets of steps on our usual route - usually going back up them on the way home, but she also did it going down them this morning. The second place is when we walk back up our driveway. I don't know why she's doing it - perhaps she doesn't want the walk to end? I'm sure she's just playing, but it can seem quite aggressive at times - she growls, pulls the lead hard, sometimes barks. I really just want to nip it in the bud before it becomes a big problem. This is what I've been doing -

1. Say 'No' firmly and instruct her to 'Sit', the run through some tricks like 'touch' and 'paw', rewarding her with treats, then I wait for maybe 10 secs or so before proceeding onwards and praising her for walking nicely.

2. Same as above, but rewarding with a favourite soft toy instead, which she then enjoys carrying all the way home. This also works well because she won't attack the lead / my trousers when we enter the driveway because she has something in her mouth already.

Although these solutions work well in the moment, in terms of snapping her out of the bad behaviour, the behaviour is still being repeated, so I don't know if I'm doing the right thing. Am I just rewarding the bad behaviour? Will she just grow out of it?

Any advice or suggestions welcome. Thanks.

Have Dog Training Questions?

Check out these introductory dog training videos...

I want my dog to stop being aggressive.

I want some help training my new puppy.

I want my dog to stop barking at everything.

I want my dog to walk nicely and calmly on the leash.

I want my dog to listen and come every time I call!