It depends on the nature of your computer network and the company's policy concerning personal email communication. Some companies have a policy that anything you send and receive is subject to being monitored and is not "private". If she is not in a position with the company to be monitoring your email, then she may very well have violated your privacy which may be actionable in court. As far as your employer is concerned, as you correctly point out, Utah, like many other states, is an employment at will state and your employer can terminate you for no reason at all. So your concern shouldn't be whether they're looking for any excuse to axe you, as you put it. They can let you go for no reason at all.