Mesh, it's a subliminal thing. Somewhere, deep in the back of her mind where it's dark and cold, a thought will fester. Over time, it will grow into an irrational concern. Eventually, it will become an unreasoning paranoia.
You see, changing the shirt implies that there could be a moment in which the target is shirt free. The implanted thought is, "What if I'm looking through the scope and catch an eyefull of moobs?"
In time, with enough therapy, she may someday regain her ability to shoot. The important thing is that she must never find out the source of that thought. That's why I'm sending this in a private message instead of in a post. We've got to be smart about this.