[Marilize]

Ok, she is used to the leash, but not to you holding it and walking with her.

Next time, don't pick up the leash. Just clip it on, have some treats or toys with you and walk away from her. If she follows, reward her. If she continues to follow you, continue to reward her. Don't bribe her though. I don't think you should show the treat or toy every time to make her move (at least, not more than a few times) because she will learn that she needs a bribe to move.

Reward her every time the leash is on her and she follows you. When she is used to this and always follows you, you can try picking up the leash. If she then follows you, make a big fuss and reward her.

This way she will learn that moving is what you want. I think that since you did so good with her training (sit, stay, wait), she now thinks that this is what you want. Since she was rewarded for sitting, staying and waiting, she doesn't understand the new concept of walking on-leash. You just need to make her understand that you want her to follow you.