If she was my dog and tested parasite negative, I would give her slippery elm (2 capsules, 400 mg ea) 2 times a day to help her stomach. I would also give her diatomaceous earth (food grade only) 2 heaping teaspoons 2 time a day thoroughly mixed with wet food. I would switch her to canned food to encourage her to eat. These suggestions are what I would do, and only if the Vet finds the dog to be otherwise normal. 60 pounds is very thin. The DE slows down the digestion and forms the stool. It helps by providing time for the food to be absorbed and increases time to digest. Look at some stool charts for dogs on the internet. If the stool is pudding like and light coloured, she may not be absorbing her food. This may be because she is passing it too quickly. That could be caused by allergies or irritable bowels, parasites or other issues. If you try the DE and slippery elm it will do no harm and you can see if it helps. You should undertake your own due diligence in following any suggestions.
One of my dogs is allergic to chicken in any form other than raw. Most chicken is intensively farmed, treated with antibiotics and growth hormones and fed pesticide laden feed. Some dogs react to these. I don't like canned food, but it is important for the dog to eat and maintain a reasonable weight. My young CC was only a bit above 50 pounds at 7.5 months (way too thin) and it took a while to build her up. She is now 10 months old and weighs about 75 pounds. She is still thin.
My young CC had the pudding poo issue also. Her litter mates were found to have giardia, and tests are not always reliable. False negatives are common depending where in the parasites life cycle they are underway when the tests are taken. My puppy tested negative for parasites, but I found her to have worms. Sometimes several tests need to be done. Normal stool should be chocolate brown, segmented and well formed, such that it can easily be picked up. Pedigree canned food works well and is very palatable to underweight dogs. It is less than $11/case of 22 oz cans at Amazon. I donate cases of it to the shelter to put weight on underweight rescued dogs. In order to gain weight the food needs to be appropriately absorbed before it is excreted. Looking a her stool and comparing it to a stool chart with images will help you.
I can't imagine leaving my CC alone for 5 hours in a crate but understand that it is necessary for many dog owners. The Corsi are a very social breed and need their humans more than many other breeds. They don't like to be alone. Five hours is a long time for a puppy, and I am fortunate to not need to leave mine for that long. If you must crate, it sounds like you need a much better crate. Perhaps go to one of the big box pet stores and get a crate which can contain the dog. I would not continue to use a crate if it had injured my dog. A flimsy crate is a dangerous crate.
Best Wishes for you and your puppy.
Ari