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Hello. I'm sorry for the long wait.
It doesn't sound like heat stroke. Heat stroke will end up causing vomiting/ diarrhea that is often bloody within an hour or two of the incident. A week later, they are either fully resolved or they had already died. I think this is a separate issue.
It sounds like she may actually have colitis. This is inflammation of the colon and they'll have the urge to go even though there may not be much in there. It could be constipation, but that's not too common in dogs. I would shoot an x-ray and do a rectal exam (along with a regular exam) to see what the cause is.
If it's constipation, then fluids and an enema should help get her cleared out. If colitis, then pumpkin and an intestinal antibiotic/ anti-inflammatory (Metronidazole) will often get it resolved.
I hope this helps, let me know if you have any other questions.