My boys scratch their top knots when they have hair in their eye, or when a hair is pulled wrong or too tight in the top knot. Make sure the top knot isn't too tight and pulling skin or part of the ears.
Could be a skin problem. Does her skin look red or irritated or flaky on top of her scalp? You could try a different shampoo, something mild and formulated for dogs. A hypoallergenic shampoo can't hurt. Be sure to rinse with clean water really well. Soap residue can cause itching.
You can also add an organic coconut oil or fish oil supplement to her diet for her skin.
The time that it will take for her top knot to grow back depends on the speed her hair grows. It's different for every dog, but cotton coats tend to grow faster.
__________________ Kristin, Max and Teddy  |