That's EXACTLY what they told me when my horse was stolen. It's a civil matter, we won't do anything. Good luck.
I got him back, no thanks to those...Ahem.
LE deals with violations of criminal law and their powers are strictly delineated by statute, and they haven't much latitude. Civil law is another matter entirely, and when a situation falls under that category the law clearly states the Courts are the arbiters in those disputes.
Now the OP's situation is a bit different than the average who owns horse dispute, these people are treading very close to extortion by threatening her. That might be something the local Prosecuting Attorney (they are the ones who decide what can be brought to a criminal trial-not the police BTW) might bring to a trial But, since she hasn't any type of written contract to back up her claim these people were only leasing the horse it walks that razor edge leaning into a civil law "he said she said"situation.
I do hope the OP gets her horse back.