Thank you for your patience. There are a number of things that could be going on here with your girl and good on you for following up on this carefully with your vet. The most common issue that can cause a bloody diarrhea like this, is parasites and thankfully the vet has ruled these out via a fecal float or something similar. I would still recommend treating your girl with a reliable all-wormer however, such as Drontal, Milbemax or Panacur to ensure there are no larval stages present at all. The next most common issue is a bacterial or viral gastroenteritis. It doesn't sound like your vet has done a bacterial culture yet, so I would definitely recommend that as the next best step here. This is typically around $150 for a full panel and is definitely money well spent.
If all is clear on the fecal culture, then the next best step would be a food elimination trial if money is an issue. It becomes quite expensive to rule out a gastrointestinal mass or tumor as ultrasound and other special diagnostic tests are required (which likely explains the estimated cost your vet gave you). A food elimination trial is cheap, but just takes time to run. Some dogs develop allergies to proteins in their food that can cause bad gastrointestinal symptoms like this. A trial with a special 'novel protein' or a 'hydrolyzed protein' diet can help to rule a food allergy in or out. This generally only takes 2 - 4 weeks for GI symptoms (compared to 8 - 12 weeks for skin symptoms), and would definitely be worth a try as the next best step here.
If in the meantime you can save up some money, a full abdominal ultrasound and contrast GI xray study would help to rule a tumor in or out. If your girl is young, then a GI tumor is much less likely. We also have to consider IBD (inflammatory bowel disease) here, however this is also hard to diagnose and typically requires endoscopy and biopsies for diagnosis (significantly more cost). A treatment trial with steroids may be the way to go if the bacterial culture is normal, full blood tests are normal ($100 - 150) and if there is no response to the food trial.
It sounds like your girl's hips are fine which is a relief. It could be that her alteration in the way she walks could be due to her diarrhea and a painful, scalded back end. Keep an eye on her wobbly walk, and if the diarrhea improves, then we would expect her walk to improve. The key worry here is the diarrhea first and foremost now, so I wouldn't keep the gait issue in the front of your mind right now.
Until you follow up with your vet, try to get an all-wormer treatment for your girl, and keep her on a bland diet until a diet trial is started. Cooked, boneless skinless chicken breast and boiled white rice is the best way to go. If your girl gets in to anything around the yard (be it objects or plants) make sure you let your vet know these details.
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