Will a prenup protect my retirement benefits?

I am engaged and want a prenuptial agreement. I have a substantial pension with a corporation I work for in Houston. My company has advised me that once I marry, my spouse automatically becomes the beneficiary of my pension. She would have to voluntarily waive her interest after we marry. I don’t want to take the chance that she would refuse to sign off once we are married. I want to advise her that I will not proceed with the wedding unless she signs a prenup giving up any interest in the pension. I am also concerned because I am told Texas is a community property state and once married, we would share everything 50/50. Will a prenuptial protect my pension in the event of a divorce?