Q. I want to help my friend with her court case, but I was told I cannot do that. Why?
This could be considered "Unlawful Practice of Law" as defined by Judiciary Law § 478:
It shall be unlawful for any natural person to practice or appear as an attorney-at-law or as an attorney and counselor-at-law for a person other than himself or herself in a court of record in this state, or to furnish attorneys or counsel or an attorney and counsel to render legal services, or to hold himself or herself out to the public as being entitled to practice law as aforesaid, or in any other manner, or to assume to be an attorney or counselor-at-law, or to assume, use, or advertise the title of lawyer, or attorney and counselor-at-law, or attorney-at-law or counselor-at-law, or attorney, or counselor, or attorney and counselor, or equivalent terms in any language, in such manner as to convey the impression that he or she is a legal practitioner of law or in any manner to advertise that he or she either alone or together with any other persons or person has, owns, conducts or maintains a law office or law and collection office, or office of any kind for the practice of law, without having first been duly and regularly licensed and admitted to practice law in the courts of record of this state, and without having taken the constitutional oath. ...
and Judiciary Law § 484
No natural person shall ask or receive, directly or indirectly, compensation for appearing for a person other than himself as attorney in any court or before any magistrate, or for preparing deeds, mortgages, assignments, discharges, leases or any other instruments affecting real estate, wills, codicils, or any other instrument affecting the disposition of property after death, or decedents' estates, or pleadings of any kind in any action brought before any court of record in this state, or make it a business to practice for another as an attorney in any court or before any magistrate unless he has been regularly admitted to practice, as an attorney or counselor, in the courts of record in the state
Also see Judiciary Law § 476-a Action for unlawful practice of the law and in Public Access Law Libraries read New York Jurisprudence, Attorneys at Law.