Well of course she is not a true salary if she is getting over time, by most of the standards I have worked under.
But as one this has happened to inthe past, unless there is a employee contract and unless there is a union, you may change someone's pay up, down, salary, and the such if you want to.
Now on the situation if this job has several people doing it, all will have to change, you can change all of your supervisors back to hourly, not just one of them for example.
But as a current salary employee, we are salary, we work for one amount, no matter if that is 30 hours or 60 hours. While the law on this may have changed, in fact when I worked for Ship and Shore as a salary employee, the fact I was required to keep track of my hours ( punch in and out) required them to pay me over time. We got a large back pay on that law suit.