Given the situation, you should ask the employee for a recertification.

An employer generally may ask an employee to provide a recertification no more often than every 30 days and only in connection with the employee’s absence. However, if a medical certification indicates that the minimum duration of the condition is greater than 30 days, an employer must wait until the minimum duration expires before requesting recertification. Nevertheless, there are exceptions that allow an employer to seek recertification sooner.

Employers may request recertification in fewer than 30 days or before the minimum duration noted in three situations: (1) the employee requests a leave extension; (2) the circumstances described in the previous certification have changed significantly, such as the frequency or duration of the absence; or (3) the employer receives information casting doubt on the employee’s stated reason for the absence or the continuing validity of the certification.

In this case, recertification can be sought before the minimum duration is reached (six months) because the frequency of the employee’s intermittent leave significantly increased and the pattern of Monday/Friday and holiday absences casts doubt on her stated reason for the leave. The employee should provide the recertification to you within at least 15 days of your request unless it is not practicable under the circumstances to do so despite diligent, good faith efforts. Any cost in obtaining the recertification is at the employee’s expense unless your company provides otherwise.