Hello Britt. This is way beyond over-the-counter treatment.
Absolutely, with her exhibiting these symptoms, she needs to be evaluated by a vet. We simply do not know the extent of what injury could have occurred. Hopefully, it is a simple soft tissue injury, but we can't assume it. What we do know is it is severe enough to result in you needing to "assist her" into a standing position, and she is refusing to urinate.
No way, would a non-steroidal medication like aspirin be appropriate in this situation.
Well worth getting a basic veterinary evaluation performed, so the problem can be narrowed down a bit and isolated.
Also, the vet carries much better non-steroidal and/or pain medication.
With these symptoms, there can also be a back injury of concern (like a person with a disc herniation in the spine).
I also would not take a wait and see approach on this. Find any vet open on Sunday.
Please let me know if I can be of any further assistance. Otherwise,
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Thanks. Dr. Andy