The statute of limitations, or time period within which they can legally try to enforce this bill, is the statutory period for a legal action based on a contract (the agreement to do the legal work in exchange for pay). If there was no written agreement, only an oral one, that is four years in your state (so she may be out of, or at least running out of time), but if there was some written agreement (like a written retainer or representation agreement) she has up to six years to take action to collect.