If you are capable of making rational decisions for the benefit of your wife, including having the ability to ask your wife's doctor any questions regarding the care of your wife, you have the right as her husband to make any and all decisions regarding the care of your sick wife, including life or death decisions. By the way, do you and your wife have a Do Not Resuscitate (DNR) document executed? Will you be able to care for your wife by yourself? This is the concern of your step-daughter, as she may think you can't, and she may be correct, especially if your wife needs help bathing, going to the toilet, dressing herself, or cooking meals, because if she can't, you msy not be capable of doing so and caring for yourself because you'll loose too much sleep and your mind will fail you due to lack of sleep. I suggest cooperating with your daughter-in-law to help lessen any friction between you and she because she is only thinking about what's best for your wife. We have a home care person caring for my wife and it's worth it to have help from a home care worker as well as a visiting nurse to monitor your wife so she doesn't have to leave home and go to the doctor. Legally, it's dependent on your capability to care for your wife and yourself. This is the time for you to listen and consider and seek the advice of others.