Before considering moving the Front Sight, Dry Fire a LOT and watch what your muzzle does when the trigger breaks. 10 Cents says it's twisting left.
If you're used to larger pistols (or double-stack Subs), the Trigger-to-Backstrap distance will be different. Combine this with everyone's hands/fingers being different sizes, there's a LOT of variables in play.
This article explains it pretty well:
10 Commandments For Improved Shooting
Boils down to Finger Placement, trigger Pull and Finger tension ('Commandments' 2, 3 & 4) are key.
You need to find which combination of Finger Placement (Center Pad vs 1st Crease, vs someplace else), Finger Pull (not slapping or jerking the trigger) and Finger Tension (not squeezing ALL your fingers when you squeeze your trigger finger) allow you to press the trigger Straight Rearward... As opposed to slightly twisting the Shield slightly left.
Some here need to move from 1st Crease to Center Pad to achieve a straight rearward Pull/Press. For others and myself, we needed to move from Center Pad to 1st crease. You (and your SIL) need t find which placement works for you.