you could ask the mother to agree to counseling. When she refuses (and I'd get it in writing somehow), then make your own arrangements for counseling. If she is angry about it, let her take it to court. She would likely look quite foolish in her rage over you obtaining services that the child needs.
Ok..so maybe that isn't the best plan. How about mediation? Mediation is free in my area, so you would file with the court to have a mediation session scheduled and bring with you the names of several therapist who you would like to use. Again...mom would look very foolish trying to resist setting up some counseling for the child.