Vomiting and diarrhea in puppy.

Lady is almost 5 months now, she's a typical Aussie puppy. She lives with me, my cousin, and her littermate Kona. We don't crate them, instead we gate them in our kitchen so they can play while we're at work. They're not super destructive, but they will pull down anything off the counters they can reach. The only time they are unsupervised is when they're in our fenced backyard, and we gate them in the kitchen at night and when we're at work.
Thursday night we had the pups at their obedience class, which is exceedingly boring for Lady. I brought an assortment of treats for her in attempt to keep her more concentrated. Some of the treats she had never had before that night. Mind you, that evening before class she ate her dinner as normal.
The following morning my cousin reported to me that Lady had diarrhea in our living room, it was described to me as very watery and left a squirt trail. She said there were four bursts before she was able or get Lady outside.
I came home during lunch to find three piles of vomit in the kitchen, she had thrown up all the food she ate at breakfast. My dad picked her up and she spend the rest of the afternoon with him. During this time, he kept giving her water and she would keep vomiting. He reported that since picking her up at 2pm, she had thrown up over 10 times within about 3 hours.
When I got home from work, I made her plain rice and put a small amount of chicken broth on the rice. She was not interested, and refused to drink any water.
For most of the day she was very lethargic.
I took her to the vet at 6:30pm the same day, they didn't feel anything in her stomach and she tested negative for parvovirus. She was obviously a little dehydrated, but not seriously.
The vet was really trying to push having X-rays done, but I really don't believe that she could have ingested anything causing blockage during the course of Thursday night.
I agreed to have her hospitalized Friday night and have her on an IV so she doesn't get dehydrated, but the vet said if she's not much better by this morning they'll need to do x-rays.
Do you have any suggestions on what other tests they should do before X-rays? I just have a strong feeling that X-rays are not necessary, and will be inconclusive. I feel like she's sick from the treats or has a stomach flu, but the vet didn't mention anything along those lines.