On Saturday, I adopted a puppy from a rescue. She's a 9 weeks old border collie/lab mix. According to the rescue, they saved her, her brother, and her sister from a shelter on their last day about a week before I adopted her. I bought the same food they had been giving her - Nutromax puppy. She hasn't eaten since we left. Yesterday, she seemed very happy and playful. Today, she seems very sad. She wants to sleep a lot. She likes it when I hold her and pet her, she starts wagging her tail pretty quickly. She will follow me around the house and come if I call her and pat my legs or clap my hands. She isn't lethargic, just seems depressed. She has pooped 3 times since getting her home - once last night and twice this morning. All 3 times, the poop was mushy, but not fully liquid. No blood, smells like normal dog poop. She is still drinking water, but hasn't eaten a thing. She vomited a couple of times, but just water and very small amounts. I would say maybe a tablepoon or 2 and it was kind of think and gooey, like snot. I know it wasn't drool, though, because I heard her gag. I got some soft food - Cesar canine cuisine. She wasn't interested. I emailed the rescue I got her from. They said the other puppies are still eating and drinking just fine. They told me to try giving her some cooked chicken or chicken soup. I made her some soup and she still wasn't interested. They told me that I can take her back for a full refund, but my family has really fallen in love with her and I want to keep her. I won't let her starve, though, so if she doesn't start eating, I might not have much choice.
I'm going to take her to a vet first thing tomorrow, but is there anything I can do for her today? Is it possible that she's just sad and depressed about being taken away from her siblings?
She has also had her first set of shots and was dewormed on February 22, according to the medical record that was sent with me.

She could miss her siblings dogs are like furry people and the vet is a good idea do you have room in your home for another puppy or even all three in case the vet can't fix the situation

Your puppy should adjust to life without her siblings just fine.
But do keep the vet appointment in order to rule out anything medical for the lack of appetite.

I have 2 little boys - ages 3 and 1 - and one puppy is enough for us. If I got another one, I don't think I'd be able to give them both the attention they deserve. The vet opens in an hour so I'm going to call then.

Homesick and missing her siblings but I would keep the vet appointment just to be on the safe side good luck.

I called 2 vet clinics and they told me that if she isn't eating by tomorrow to take her in, but not to worry at this point and she has started to eat a little bit.

Thanks for the update, I am glad she is starting to eat for you. Keep up the vaccine schedule so that she is properly protected against things like parvo and distemper. And best of luck, enjoy ALL your little ones. You must really have your hands full, but ain't it great?

Yes, its really awesome. She's eating now and she has a lot more energy. She's more playful and seems much happier. I guess she just needed time to adjust. I have an appointment for her 2nd set of shots next week.