Why is my 4-month-old puppy not eating, not drinking, and so sleepy?

Hi there! I'm very sorry to hear about Kimi's troubles. If I had a client call and report the clinical signs you are describing, I'd ask to see the puppy right away. Young puppies, especially smaller ones, can be susceptible to getting a low blood sugar if they go a long time without eating. Not to mention that they can get dehydrated fairly easily as well.
I'd definitely recommend Kimi go in to see her veterinarian right away. The veterinarian can perform an exam and check her hydration status. They may also want to check Kimi for an infection of some kind, and/or evaluate some diagnostics like radiographs and lab work.
Kimi may need some in-hospital treatments or even just some medications for you to give at home.
Things that can make puppies not feel well and stop eating include, but aren't limited to viruses, baceterial infections, ingesting toxic materials, ingesting pieces of toy or blanket and getting a blockage, eating anything out of the ordinary and getting indigestion, or even parasites.
I hope you find this answer helpful. Best of luck!