SoCalGirl, pretty much hit it on the head. A key component in becoming “national” is having your business side in order and being a legal entity. It would involve being incorporated according to the laws of your state. Those laws definitely vary from state to state so you may find an attorney helpful. Things to include are national officers and/or a board of directors, a tax ID number, and liability insurance. Your alumnae association can be a valuable asset in getting these things together. Rally them.
Here is a list of some sororities with less than 15 chapters.
Kappa Beta Gamma –
www.kappabetagamma.org/
Arethusa (Sigma Gamma Phi) -
www.arethusa.org/
Agonian (Alpha Kappa Phi) -
www.agonian-kappa.org/
Clio Sorority (Phi Kappa Pi) -
www.geneseo.edu/~clio/
Your president and chapter adviser really need to sit with the Greek Adviser. Have the GA outline in writing what is expected of your chapter. Only then can you determine what to do next.