To me the Before and After look so different that I’d do a bute test first. The mare looks so different behind, all the way up to the SI joint. Her demeanor looks different: Her tail is relaxed and she never gets “stung” and takes a short step and/or kicks out. Note that she does swish her tail the whole time in the “after” footage.
And my vet would have prescribed more that 2g/24 hours. The point is to kill pain “dead” so that you can take it “officially” out of the equation. For a large horse, the dose might be 2g AM and PM for 5 days. Ride all days, but really pay attention to any contrasts you see between day 0, Day 3 and Day 5. The 0/3 comparison tells you how much pain was involved because you are comparing no bute to Ahelluvalotofit. And comparing Day 3 with Day 5 tells you if riding is making the problem worse or whether it’s staying the same and not piercing through all that bute.
This isn’t the only way to do a bute test, so certainly ask others for their protocol. I hope you can find an answer, OP.