When sheik jumps, the range that is covered by her needles at any point when she is in the air. It makes a triangle. Do I need to like... draw this out or something?
Anyway, after establishing the triangle, basically what you do is pressure into it to a point where, after she lands, she would almost be able to reach you with a dash attack. This creates a rock paper scissors game where, if she jumps again, you can jump forward and hit her, or if she goes for a dash attack/grab, you can hit her. This is the safest pressure area I have found vs Sheik.
Additionally, if she goes too high and the area of the triangle is increased to a large amount, you can run through the limit of the triangle and position yourself underneath Sheik.