I might be completely wrong, but is it possible to do this as a reset?
b+3 2, b+1 2, 3 1, EX scream jip b+3 (reset) b+1 2, 3~scream (jip) f+1 2~hair whip/ step up= 51% total
I really only had the chance to test it on one person so far, a noobier guy, and it worked. You can probably easily block the b+1, but do you think it could work on a more experienced player?
that actually might work on a more experienced player who knows sindel's B3F2 combo has an overhead in it. they'll block high not expecting you to end early with a low hit. she can also cancel low fireball or xray from B3, though.
a more appropriate reset would be, for example, B3, f2, dash, 3, yell, jip, F1, 2, dash [reset] B1, 2, dash, 3, yell, jip, 2, 1, hair whip.
F1, 2 offers a stagger-like animation similar to sub zero's and cyrax's. it's more for people who don't know what it does or think you'l link a special move after it. i'd only try it once, maybe twice in a match unless your opponent is clueless.