Generally, an undivorced spouse can make medical decisions for an incapacitated or unable-to-communicate spouse, even if divorce was filed for: until the divorce is final, the two people are still spouses.If your mother was stiill competent or communicative, she could draft a medical power of attorney (also called variously a medical proxy, an advance directive, or a "living will") which could both set out her wishes or instructions and also designate a person or persons to make decisions for her at need. But if she already incompetent or uncommunicative, she cannot do that.Even though her spouse may be able to make decisions for her, he needs to make them in accordance with her best interest. If you feel that he is not, you could bring an legal action in family or chancery court to have a legal guardian appointed for her (e.g. you, if you are an adult [not  minor]), with that guardian being given the power to make decisions on her behalf. You'd have to be able to show in court that he is not making decisions in her interest, however, to do this. If you believe this is the case, or you want to explore this option, meet with a family or elder law attorney to discuss what you'd need to do.