Oh I am so sorry that you have been going through all of this with your new puppy. PLEASE~Do NOT believe anything that a Pet Shop tells you to do! They are horrible places that sell puppies from mills and your little one is no exception.
She could have any number of illnesses that have been missed at your vet. Kennel Cough does not cause bloody foul smelling diarrhea!
If she had been having blood and mucus in her poop since yesterday this is an emergency and you need to take her to the ER vet now. I have no idea what is going on with her but it seems to me that you are not getting the answers that you need to have a health puppy. Please take her immediately to your nearest ER for treatment. Once she is on the road to recovery I would demand a refund from the pet shop and payment of all medical bills.