Why can't I do this gracefully for my mom?

ok, mom with copd, doesn't think she can visit doctor due to her SOB. She has had 3 exacerbations/pneumothoraxes since January(10 months ago). She gets SOB just from eating. We wheelchair her from bed to kitchen, where she wants to sit all day at the table and have the TV in there on at a very loud volume. She takes 37.5 mg of prednisone daily. Our efforts to wean were unsuccessful. So now, she has the COPD which led to cor pulmonale, which led to right sided heart failure and atrial fibrillation. When her prednisone was at 40 mg, she would slip into symptomatic a-fib with a rapid irregular heart rate. 37.5 mg seems to be her magic #. Starting in September, she now has pedal and pre-tibial 3+ pitting edema. I have been staying here with her everyday since she was first discharged from hospital in January. I just happened to be without a job in January, and am RN. My only sister and sibling had a job. So, I arrive every morning at about 0600. She has had history of dyspnea just after getting out of bed. I stay until 1600, when my sister gets off work. She stays till my mom goes to bed @ app. 1900. Sister lives only 10 minutes away, I live 20 minutes from our mother's house. So sister covers overnight. Then I usually have Saturday off and sister has Sunday off. This puts me with my mom for about 60 hours per week, my sister does about 22 (plus her full time job). We have consulted hospice (her pulmonologist was glad to order). But, since my sister wants her to have "happy days", we have not discussed the hospice since their initial informative visit. My mother and sister obviously expect me to be here every day, and to sit with her at the table the whole time I am here. (Mom will go to couch to elevate feet for sis, but not for me.) I feel overstimulated by the constant blare of the TV, the noise of the dehumidifier and the oxygen concentrator machine. Also, the chairs are very uncomfortable for me (herniated L5-S1). So, if I go and sit in the living room, not 20 feet from her, she acts out like she's mad at me. I am certain that I have "caregiver burnout".
I have asked that we bring someone else into the rotation, and she immediately becomes upset because she doesn't think someone besides us can help her through her bouts of SOB/dyspnea. I also feel guilty about asking for this help because she will have to pay for it. I am starting to resent my sister, my mother's sisters (never helped with her or her mother), and my mother. Sometimes she won't even lift her arm to get her robe off, even when I know she can do this without becoming SOB. I don't know who to talk to. My husband is RN as well, and appears to have no empathy for me whatsoever. He will ask how I am, but I can tell he really doesn't want to hear the answer. (His mother died just one year ago in home hospice for Alzheimers. I helped his family care for her in her home during the last month of her life.) I can't talk with my sister, because she will just think I'm trying to scoot out of my responsibilty. I cry all the way home every day. I am seeing a therapist who has me on high dose of SSRI antidepressant and mood stabliizers. She validates my feelings, but it's not enough. She tells me that I am in constant agony and she is right, but I can't seem to feel better. Now, mom's abdomen is distended, and I don't know if it is just more edema or liver failure, because we are all afraid to make a trip to the doctors' office because we fear a large dyspneic episode. Why can't I selflessly sit next to her all day like my sister does? I'm the nurse; she's not. WTH?