How do I keep myself sane and my marriage intact while caring for my MIL?

We've been married less than 5 years. We live with my husband's Mother. Not cause we can't afford a place of our own. But because MIL can't afford things on her own. She does not care about anyone but her self. I took over making sure her bills got paid every month when she gets her check. Cause she would not do it. She had been lieing to my husband for 2 years about paying the insurance on the house before I came along. He was giving her the money and she pocketed it. She will look you in the eye and lie ALL the time. None of her 3 siblings have anything to do with her. And on the rare occasion that my husband does say anything to her about her behavior she will stalk down the hallway cussing like a sailor and say she will kill herself. She talks on the phone to her friends and her Aunt. She tells people our business. Plus she lies to them about us. She will love you to your face and talk about you like your filth behind your back. I'm at my witts end here. I do all the cooking, cleaning, taking her to her doctors appointment s. She is diabetic so I've changed a lot of the way I cook. Plus I've changed things that she is allowed to eat. She is the most unappreciative person I've ever met in my life.