You really don't want to get that center section of the tip notch much less than 3/8'' if possible, but i've filed them down to 1/4'' thickness before doing the same thing you are doing. Make sure the top of your tip notches have a tear drop shape and is rounded over evenly..... Also round over the notches coming into the belly side of the limb tips and eye ball them to see the string is laying evenly on the limb where the loop comes together.....
I know this may sound strange.... But try flipping the loop on your string 180 degrees too. i've seen this effect tracking on recurve limbs that are sensitive to perfect alignment and fixed the problem.
If everything has already been done and she is still twisting you will most likely have to live with it on a one piece bow.... trying to straighten it by twisting the limbs and heating them will bring a bow back to straight and stay there if it was built straight to begin with.... but... if you have built in a twist somehow, or failed to get the profile straight, the twisting of the limbs will not hold for long.
If you have a TD bow, you can play with shims on the limb pads to bring the tips over and get things straight again.......
If you are having sensitivity issues with limb tracking and limb stability. it may be wise to to address the taper rates used and get a bit more beef in the outer limb. Sometimes just changing the stop location in the form and cutting back on the reflex tip location can make a big difference too. It's the limb thickness that makes your limb stable and it's 8 times stronger than adding width for stability. food for thought. Kirk.