I have 10 week and a 9 week old border collie puppies, the 10 week old usually can't wait to get her food. Yesterday she stopped eating and now won't even look at food. Help

How is the pup acting other than not wanting to eat?
Still playful? Not lethargic?

How is the stool? No loose bowels?
No vomiting?

Have you tried a different food to encourage her to eat?

Sorry to answer with more questions.

She is a bit lathargic but still likes to play a bit. Her stools are fine. We have tried other dried foods and treats but she's not interested.

Try the roast chicken test, not many dogs can resist roast chicken, even if they aren't feeling their best, and then as annoying as it is to hear this suggestion, I would take her in to the vet for a check up.
It could be something as simple as worms making her feel a bit off her food, but I would hate to tell you to wait it out and it ended up being something serious...

Thanks for your help, I will try the chicken.

Could she be in pain from a non-obvious injury such as a blow to the side? Could she have eaten anything inside or outside, from pills or chocolate or a small toy stuck in her esophagus (I had a very sick dog who managed to eat some used tea bags).
Paying the vet is the next step in a day or 2.