I say turn her in.
I busted one of my coworkers last year for this. She was responsible for administering the timekeeping for our company. She had the ability to adjust and edit clockin/clockout times for everyone in the company, including herself. As one who manages projects -I have the ability look at everyone’s timesheet to see they are charging time to my projects (look only-no edit capability even for my own time), and I noticed this person would stroll in late everyday and also take a half hour extra for lunch than what was recorded. I held my tongue for months thinking that someone else would notice, but the time cheating went on unabated, so…
Finger pointing and tattling are frowned on in my company. I typed an anonymous note and placed it on the HR manager’s desk. Within days, the cheater’s timekeeping responsibilities were taken away.
If you do tell -stay anonymous. Avoid crossfire and repercussions.