How to get married without losing our Social Security benefits?

My girlfriend is on SSI, I'm on SSD. She is dying of advanced cancer. We very much want to be married while she still has some time left. Problem is, both of our incomes are meager and we can only just afford a small apartment with our combined incomes and without her medical, she will quickly die an agonizing, painful death with no home. How can we legally get married AND keep our benefits while she lives out the remainder of her days?