My dog hasn't pooped in almost two days. ?

I apologize ahead of time for the length of this question, but I want to make sure the details are there. My 1 1/2 year old, 25.4 lb. Dachshund/Beagle mix has not pooped in nearly two days. I brought her to the vet the day before yesterday because she was infrequently vomiting small amounts of her dry dog food (Purina Beneful: Healthy Radiance). The vet gave her an antacid injection thinking it might be acid reflux because she showed no signs of pain anywhere and her behavior hadn't changed at all. When I brought her home, she had no interest in eating. I contacted the vet and she told me to feed her a beef and rice diet for the next few days starting the next day. So, she didn't eat for one full day. I've been giving her the beef and rice with half a Pepcid AC tablet as the vet has recommended. She's had three full cups so far and hasn't pooped once since I began. I had her in her crate today for about five hours while I was at work, and she has eaten her own poop before, but there's no way for me to be sure that's what's happening. Also, the ground has been covered in snow. She seems to love it, but maybe she's hesitant to poop in it? Again, she's in perfect spirits and doesn't seem to be in any pain. Any ideas?