You might want to try warming up for a looong time every ride. Spend at least fifteen minutes flexing both ways.
When you turn, use both legs. Use your inside leg at the girth, and your outside leg behind. The outside leg will bring the haunches around and flex the body; the inside leg will provide a "pole" to bend the body around.
After doing round circles for about five minutes in each direction, ask the horse to open and close the circle. Do this by pressing more firmly (sometimes press-release-press-release, depending on how yor horse reacts) with the inside leg to open the circle, or more firmly with the outside leg to close the circle.
You will know you are getting somewhere when the horse crosses her legs as she opens or closes. For example, as you open the circle, she will take her inside leg and put it almost in front of her ouside leg as she widens her turn.
Don't even think about trotting until you can get a smooth turn, open, and close, both ways. Don't even think about cantering until you can flex smoothly at the trot
Your horse will be much more balanced and more responsive to your leg aids.