RE: Wife having problems grouping with new bow
I would definitely start with new nocks & go from there. You may find that takes care of a lot of the problem.
Another suggestion as far as releases would be to check out some type of thumb trigger release. Sort of the same feel as pulling with fingers, but with a mechanical release so it might be a bit more consistent. Just a thought.
One other thought....
Doesn't an arrow when shot with fingers tend to exert some side to side pressure? Maybe the softer bristles on the sides of the newer biscuit aren't strong enough to stand up to that force? A call or email to the WB people may answer that question.