Thanks @Mike McCarthy for the quick response.
I know there was a blockage - she has admitted to that. So definitely something she shouldn't have flushed. This is the 2nd incident with a toilet blockage for her, but different toilet. The first one happened shortly after she moved in (10 days) so we gave her the benefit of the doubt for that one, and hired Roto-Rooter for that one.
I agree that we should've noticed the missing nut on the bolt during the changeover, but some things get missed. She stated that multiple guests have mentioned the toilet, but she failed to bring anything to our attention.
We will definitely be replacing the wax ring and securing the bolt. That's not an issue. The issue is the damage to the ceiling and/or any other damage. She also notes that she noticed a ring around the light fixture. But I have pix of the house before she took possession, and there was no water damage ring. So another item that pointed to a problem that she did not bring to our attention.
I believe that if there is an issue and the tenant does not bring it to our attention to fix, that resulting issues are most likely (and in this case) the responsibility of the tenant. Also, my lease states that the tenants are responsible for plumbing blockages.