First off Carrie, I am very sorry for your loss. Saying goodbye is always difficult, more so when you dont know exactly what happened.
As I read your question I too first thought of a urinary tract infection. The initial symptoms fit however it would not have been fatal. A considered diabetes as well. Diabetes causes an elevation in the blood sugar levels and results in excessive urinating, urinary tract infections, and weakness. Once you mentioned the extreme amount of blood during her final days I knew that this was likely a common urinary tract cancer called Transitional Cell Carcinoma (TCC). TCC is more common in older dogs however can be seen in dogs as young as 2 or 3 years old. It starts of as an infection and then causes urination troubles, pain, weakness, and eventually a lot of bleeding.
My condolences to you and your family, I hope this helps a little with closure. TCC if very difficult to control and cannot be cured.
Thank you so much for responding! Your comment helps alot! I have been wondering for a while if it was maybe some type of cancer.
maybe this was the cause of her death. Thanks again!!