Hi,
I agree that letting a dog who has a strong chase instinct is asking for trouble. It is a good idea for Daisy to make friends with delivery drivers but you have to see it from her point of view - it's not the people she is chasing off but strange smelling noisy things that run away very fast when she has a go at them. How satisfying is that? Mega! And it works every time! Add to that the pack leader rushing out every time it happens and adding their voice to the onslaught and Daisy probably thinks she is part of an unbeatable team!
I must admit this is a tough one to cure because her behaviour is rewarded by the truck leaving every time but it can be done. The best solution has got to be building her a safe enclosure for when you can't be with her and especially at night. The alternative is serious injury or worse for your dog and possibly heavy legal fees and enormous guilt for you.