It really depends on your age and activity level. For people who lead more sedentary lives, you can live without an ACL just fine...and a course of PT can help compensate for a torn ACL within parameters. For instance, in a closed chain position (foot on the ground), a strong hamstring can prevent the tibia from translating too far forward (normally a job for the ACL).
Yet, I still think that you've had a recent change in your pain levels and the PA should not be the one ultimately making this decision. The decision on whether or not to have an ACL reconstruction is best done by getting all the recent information by a well-informed expert...ie, an orthopedic surgon.
To say the very least, I think a course of PT is acceptable...in fact, if you are considering surgery, it's usually required prior to surgery anyway...so go ahead and get a leg up (no pun intended)...if you feel better with PT, then way to go...if you need surgery, you'll be one step ahead.
I'd also recommend that the PT rule out the pain coming from the lumbar spine if you are having it in the entire length of the leg.