Does a Realtor HELP or HURT when buying a Spec Home???

I will be relocating to a new city within the next 2 months. We have decided 2 buy a spec home in a new fast growing community. Prior 2 having my realtor I had already visited & done some research of my own in this area, now that my realtor (which has gone out home searching for me only twice- pre owned homes only) wants 2 be part of the process& continuously warns me not 2 visit them without her & reminds my husband and I how much we need her! As soon as she knows a builders has contacted me she intervenes & I lose all connection. When the builders talk a price she tells me they are at their rock bottom price& cannot go any lower.. Needless 2 say after I contacted them directly they offered an additional $2000 towards closing cost! I am afraid she will not work to get me the best deal possible & she intimidates the builders &they will no longer want 2 negotiate with me. WHATS HER COMMISSION PRICE& IF I CUT CONNECTION WITH HER WILL THE BUILDER BE MORE WILLING TO NEGOTIATE WIH ME?