In my view, the more accurate thing to say is: If you are a MESOMORPH, and you do HEAVY, HARD squats, your legs MAY get thick.
Mine DID get big--1.5 inches bigger after maybe two months of squatting about 105 pounds (45-pound bar, 60 pounds in plates. Not quite my weight.) Maybe it's because I put on muscle very, very easily. Some women do. Some of the women here may be among this group.
I talked to a well-known powerlifter who writes for M&F (I emailed him and he was gracious enough to talk with me on the phone for 20 minutes) and he told me to lay off the squats and to do isolation moves once a week. My legs have deflated by 1 inch. They'e STILL firm, but they look much more proportional.
I don't have half the knowledge of the women on this board, I realize. But I know from PERSONAL, if not PROFESSIONAL experience: When you go heavy and hard on the squats, female legs can get big. Why else would y'all continue to do squats if they didn't?
I'm not saying NOT to do squats. They do make your butt and legs firm. But watch your progress very carefully.
One more thing: There's middle ground between lifting pink dumbbells and lifting huge amounts of weight. Everyone is going for a different look and has different goals. I've heard it here often: What works for one woman isn't going to work for every woman. You've got to tweak, and modify, and try new stuff. Maybe for some women, it involves heavy squats--for others, it means backing off a bit.
Just one woman's experience.