Definitely consult with your lawyer before you do anything. But just a thought: What I'm reading is that your sister is court ordered to take your mom on weekends. She has not complied with this court order but she does visit your mom on weekends. Because your sister has refused to take your mom on the weekends you have prohibited your sister from seeing your mom at all.
Two wrongs don't make a right and before you find yourself in legal trouble yourself it might be a better idea to just let your sister visit while you talk to your attorney. It's not your job to punish your sister for not doing what you want her to do. If she's violating a court order let the court figure it out. And be the bigger person by letting her visit her mom.
Look at this a different way. When couples divorce and have set-up visitation and don't show, all the Court cares about is if they are paying their child support. Talk to your attorney. But don't cut her off from seeing your Mom. The person it hurts most is your Mom.
BTW: I too have a Court order re my brother. He assaulted me last year. I had to decide what was more important to me: the hospital bill or her I chose her. But he's been a complete jerk, and rarely follows the Order. When he actually speaks to her, he makes shitty comments about me, as well as scheduling to see her (when it is required he give ME 24-hour notice. A third-party must also be present. He doesn't follow it. I'm also concerned about his negative and hateful comments about me (and when I've been her, he calls me crazy, fat and stupid in front of her), I don't do that (though I'd love to). Before Alzheimer's, I was the child who made an effort. He barely called or saw her. UNLESS it included money or mooching off her and living here. Time to get an attorney again. I hate this. I've made more gestures to at least attempt to get along: counseling, agree to disagree, whatever. His ego and anger are more important to him than our Mom. I'm probably going to file another Temporary Restraining Order and find an attorney again. This is childish. I want him to adhere to the agreement and STOP MANIPULATING OUR Mom. He hasn't even seen her this year, but has called Adult Protective Services on me twice with lies. No more. K
Two wrongs don't make a right and before you find yourself in legal trouble yourself it might be a better idea to just let your sister visit while you talk to your attorney. It's not your job to punish your sister for not doing what you want her to do. If she's violating a court order let the court figure it out. And be the bigger person by letting her visit her mom.