Hopefully she isn't pregnant from a gelded yearling! Separate them, and get a decent vet out to run blood tests to see if something shows up there, test her back to see if there is any spinal damage and generally try to get to the botom of this. Look at the pasutre and see if you can find any poisionous plants, or even see if someone might have dumped something on your land. If the pasture is sparse, make sure she has ad lib hay so she isn't tempted to eat poisinous weeds.
Hope you get you filly sobered up soon!
We lose ourselves in the things we love, we find ourselves there too ~Kristen Martz