Answer:
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For Building Muscle, Getting “Toned,” And Improving How Your Body Looks… Resting 1-3 minutes between sets is probably ideal for you. The higher your training intensity is for a given exercise and/or the more demanding it is on your body, the more you should stay nearer to the 2-3 minute range.
My guess would be stretching in the leg she wants to improve. I have done this many times and stretching would be the best way.
You can go into a split and then lean as far forward as you can.
Another one is to when in the split grab your toes and pull up,stretching near the actual foot which then gives you more of a chance to lift your leg higher.