What options do I have in removing a dangerous animal off family property

Property owned by him before new marriage with his and my horses living on it. I am owners daughter and have been taking care of all horses, in charge of their care Her horse brought there with permission from my father Free board and no formal agreement for past 9 mo, I have pd its feed, hay, farrier and vet costs with no reimbursement Gave her 30 days to move horse because she's a danger to the others and people (this was not disclosed beforehand) Refuses to move it