How do you stop squeaky leather ladies shoes?

Leather squeaks because it's stiff and while chemically softened will make that terrible sound when coming in contact with itself...friction. Yes, you can treat it with talcum on the inside but for its easy to just stretch out the friction that's causing the squeaks, try bending and twisting the sneakers as much as possible each time you put them on, this will make the leather more flexible and while it may not completely remove the squeaks altogether (that will come in time) it will break the leather in enough that the volume of the squeaks will be noticeably reduced until it's no longer squeaking at all.