Cruciate ligaments stabilize joints that have a very large range of motion; they don't really restrict the range of motion of the joint outside of this stabilization. A knee with a healthy ACL is going to have the same flexion/extension ROM in their knee as a person with a fully ruptured ACL — the limitation in knee ROM remains compression of the hamstrings against the calf. Non-exercise activities (like dance) will be challenging the knee now, as it is less stable against rotational forces.
An ACL tear means a reduction in knee rotational stability, so the exercise goal is to increase knee stability without applying unnecessary torque:
Strengthen the Hamstrings;
Perform full range of motion leg exercises (lunges, squats);
Loosen the IT band;
Loosen the piriformis; and
Strengthen the glutes.
What you're really trying to do is build legs that are strong, mobile and straight
. If your leg rotates externally at the hip, it's going to put rotational force on the knee. If your calf rotates internally at the ankle, it's going to put rotational force on the knee.
(cannibalized a little from a previous post I made on ACL tears)