I am so sorry you lost your Bella. Please as Barney suggested do a lot of reading here first prior to purchasing another puppy.
If you go to
www.ytca.org, that they recommend pups do NOT leave the breeder prior to 12wks old And weighing two pounds.
With any puppy, but especially toy breeds, the first few months of life, can as you have seen, present challenges to the owner, medical emergencies, training dilemmas etc.
I do encourage you to set up an emergency fund prior to purchasing any puppy, and also consider pet insurance.
We can not know if you had hospitalized her she would have survived. I am assuming you didn't have a necropsy done, in order to determine the cause of death.
For sure your breeder needs to be aware of what happened here.
Once again my condolences.