I would be most concerned that you're seeing an injury. Spinal injuries, hip problems, luxating patellas and torn cranial cruciates are all common in this breed.
Dogs cannot take ibuprofen, tylenol, aleve or motrin but some aspirin may be ok.
You can read about the precautions and get dosage information here:
But there are other medications that are much better for pain so only make this a temporary solution.
Let me know if you need more help.
Any time that a dog has loose stools, you have to look for a cause of the stomach upset. It might be as simple as them having stolen something from the trash. I would want to keep a close eye on it and see your vet if the diarrhea persists or there is little improvement.
Keep in mind that when dogs get diarrhea, their anal glands fail to empty as they should. So, this can cause pain around the tail. If this is the case, your vet can express the glands and give her some relief.
If you like, you can put her on a bland diet like boiled chicken and white rice. This helps to settle the stomach and firm up the stools.
Let me know if you want to discuss this more.