A: Thank you for being such a devoted parent to both your kids; the efforts you put forth for their well-being and happiness are beyond what many parents without special needs kids could ever imagine. Sibling rivalry is tough even when there aren't extenuating circumstances of the kind in your home.
I recommend a two-pronged approach. First, teach your 9 year old to help care for your 14 year old in an age-appropriate way such as reading to her sister, holding her hand while watching TV, and even feeding her with your supervision. Make your younger daughter's efforts the subject of high praise and positive reinforcement. Second, find enough help from other family members or friends to give you more solo time with your 9 year old. Or you may consider paying a professional caregiver to take over some duties a few times a week. Your younger daughter needs to know that she is worth the extra effort you are taking to find other help.