My legs are stronger than I thought from walking and hiking in the mountains. I've already increased my leg weights up to 20 pounds. How can I add more weight for my legs? Are there ankle weights that are heavier than 20 pounds?

Don't go above 20 pounds with the ankle weights - heavier versions could become a problem orthopedically. If you outgrow your weights, switch to exercises that use your body weight for resistance, like modified squats and lunges. These are standard exercises, which you can find in many books. One good source, which has a lot of lower body exercises, is Complete Book of Butt and Legs by Kurt, Mike and Brett Brungardt (Villard Books); it's available from Amazon.com if your local bookstore doesn't have it. Another option that's practical for some women is to use strength training machines. Because you're held in position by the machine, you can safely lift heavier weights.