With a torn ligament, surgery is a must. One of my fosters (Isabella) had this surgery done in September and she was cleared medically in November. I worried the entire time during her recovery because she is a very active pup. She hated being crated, so I opted for a small area for her. Also, when I was home, I allowed her to sit with me.
Total crate rest for her would have been more stressful than what I did.
Before you know it your Bella will be good as new! The time goes quickly.