Run, don't walk, if a photographer declines to provide you with references. If she does give you a list of names and numbers, do your due diligence and talk to these former clients before signing on the dotted line. Previous brides can dish on the things they loved, hated or felt ambivalent about in regard to their vendor.
Since most of the contacts she provides you with will be satisfied customers, make an effort to ask around among your friends and family, and check to see if anyone has reviewed her services online. Good news travels fast, but bad news is even speedier, so anyone with a tale of woe and disappointment is usually going to be willing to dish details.