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If you don't know if she is salaried exempt, she's not salaried exempt. You would have established her as a salaried employee, noting that she would receive the same amount of pay regardless of the number of hours she worked in a day (meaning she'd get her full salary even if she worked one hour in a day).
Additionally, she does not receive sufficient pay to be legally considered a salaried exempt employee under current law and you have her pay set by the hour, not in a weekly salary.
She is an hourly employee then and is legally required to be paid overtime when she works more than 40 hours in a week, even if you did not authorize it. You have other means to keep her from working overtime, such as reducing her hours the following week to make up the difference (she works and is paid less) or other disciplinary actions if she continues to not follow rules you set about overtime. However, once she has worked it, authorized or not, it must be paid at time and a half.
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