Thanks for the additional feedback, it's helpful but I still need to know a few more things:
Has she ever been tested for intestinal parasites (ie, a fecal sample for worms, etc)? Or has she been thoroughly dewormed or on monthly dewormer (eg: heartgard, interceptor,etc) --I'm asking because certain GI parasites can cause upper GI bleeding.
Also, if you can let me know the ingredients in the weed killer and the pesticides used, that would be VERY helpful and I can do a websearch on those ingredients to see if they can cause bleeding and/or GI distress. Sometimes it doesn't take much to cause an adverse reaction.
Rottweilers are a breed that's genetically prediposed to a type of bleeding disorder called Von Willebrand's Disease and some never show symptoms, while other do at unexpected times (this shows up as blood loss /bleeding tendencies ...so symptoms that suggest bleeding into the intestines could make us consider whether or not she may have a form of VWD). The only good way to diagnose that is by a blood test sent to an outside lab, and the results take several days or more. This would be a less likely cause of her symptoms than intestinal parasites or toxins.
Lastly, however, your mentioning she (like lots of pups) is known to eat/swallow items concerns me greatly that this may be the cause of her symptoms. If she has a full or partial intestinal obstruction, time is of the essence to have this diagnosed. This is done with a combination of physical examination, x-ray (sometimes with barium), and/or ultrasound. Over the past couple of decades, I could write a book about some of the odd things we've retrieved from the GI tract of pets...Barbie Doll arms, underwear, washclothes, tampons, rocks, acorns, zippers, popsicle sticks, Greenies, rawhides, chew-hooves, bones, and the list goes on and on....
Whenever a usually healthy pup refuses food for more than one meal, I would start to become concerned , especially with your details indicating she is known to ingest non-food items....
If you want me to check on the pesticide/weed killer angle for you, let me know, otherwise if this answer gives you enough information to act upon, please "accept' this answer (or ask follow up question),as well as provide me with feedback! Thanks so much!