Horrifying yet . . . typical. I know a fit woman in her 50s whose doctor wouldn’t recommend physical therapy when she tore her meniscus because, he said, “You’re old. Physical therapy is for young athletes.” When she said: “But I want to play tennis and ski and hike again” he replied: “Maybe you should find something else to do.” To which SHE replied: “Maybe what I should find is a new doctor.”
You should also inform your doctor that there is lots and lots of evidence that lifting weight is actually very important for women as they age, helping to maintain bone density and prevent osteoporosis. If you want references of scientific studies, just let me know -- I can provide the ammo!
I’m new to Crossfit, too, but my own experience with funky knees has shown that there’s a lot that can be done. I was pretty hard on my body in college and have missing articular cartilage and had to have double arthroscopies to drill holes to create scar tissue many years ago. For awhile after that, I tried to be a good girl and avoided exercises said to over-stress the knees . . . and they hurt like crazy. But when I started doing squats, wall sits, kettlebell swings, step-ups and even pistols – with tons of focus on form, form, FORM – plus lots of yoga standing poses, my knees felt way better. Of course, your mileage may vary. But it's good to trust your own experience.
You can always try adding exercises that develop the musculature around the knee and simply back off if you feel like you’re getting inflamed. You might be pretty surprised!