I've injured my ACL twice. The first time it was a complete rupture with a lot of cartilage damage. I was in a knee immobilizer for a week and a half or so before I started to walk on it. Probably could've been sooner, but I was a bit gun shy. My knee buckled again right afterwards. I was immobilized for maybe a week or two after surgery, but I was out of it at times for therapy. I can't remember how long until I was walking without crutches, but it wasn't more than 2 weeks. I had a patellar graft, which actually resulted in the most pain post-op.
The second time was just a tear. I was never in an immobilizer after the injury. I walked off the court and went to the doctor a few days later when it wasn't getting better. I was in an immobilizer for 1 week after surgery. I actually had two surgeries that time. Had no ACL after the first surgery and was walking within a few days. They were bending it in therapy the day after the second surgery when they put the ACL in. That one was a graft from a cadaver.
Long story short, ACL injuries most likely don't result in a long time in an immobilizer. Definitely won't have a cast. Her not being in one doesn't say anything about how her recovery is going. That being said, she's younger than I was when I had my injuries and she's also a much better athlete. I wouldn't be shocked if she was playing in November/December, but I would be shocked if she was 100%. She never ceases to amaze me, though.