About churches making you feel sick and sweat a lot. These are the key symptoms of anxiety. You are uncomfortable there mentally and emotionally, no? I get uneasy around crosses too, but it isn't because I have a demon in me, it's because the image of a dead man that was tortured being hung as an ornament on the wall just doesn't sit right with me. I think it's extremely morbid and disrespectful to the dead. The "thought of holy water" should also give away that this is entirely mental. A thought of something holy is not going to somehow have power to repel you. Perhaps you should analyze what it is about churches and crosses that causes these emotions in you. People these days rarely consider their thoughts and emotions and it's very unhealthy. I would say that you should consider soul searching and finding a faith that makes you feel good and secure.
Magick has no color. There is no black and white, or rainbow for that matter. It is important to learn about magick as a whole and not worry about color. Life is a double sided coin. Someone that heals can cause disease and injury. Someone that blesses can curse. These are not separate, they are merely different applications of the same knowledge and methods.
And lastly, the hospital gown gives away that this was a spirit of the dead, a shade, a lost soul, a "ghost", whatever you wish to call it. How many people do you think die in hospitals when they have unfinished business? How many people do you think die in hospitals with no one to mourn for them? No one to care? How many die there with mental illnesses, alone and scared, hoping that they can live just a little longer so they can make a change, do things differently? Can you now imagine, how many souls roam our plane after they die in a state of pure hatred, anger, and sorrow? If you believe that people that die after living an isolated or ignorant life become "demons" then yes, the women was a "demon". I wouldn't quite call her that.
But this spirit of the dead is far from powerful, and if you feel she is around you still, then I suggest that you not fuel her negativity with more negativity, but instead, bid her peace and bless her, give her an offering of gratitude for her departing from your life. See if she leaves. Sometimes it's all that is needed. But if that doesn't work, banish her and call in a psychopomp to drag her to a place that she can snap out of her delusions.