Coworker’s time theft negatively impacts me?

We work 4 days per week and have set hours we must bill hours each week in addition to documenting every client interaction.

My coworker consistently meets productivity expectations, but also secretly works a fifth day. On paper, it appears she’s meeting these hours in 40 hours. Truly it’s closer to 55-60 hours.

I have strict work boundaries. I only work 40 hours. I consistently do not meet the billing standards. I am regularly 30 billable hours behind my coworker each month.

This reflects poorly on me. I am constantly being compared and scrutinized for not meeting similar billing as my coworker.

I have not outed her because it feels petty.

There is no way without matching her hours that I can meet this standard. I am not paid for 60 hours, nor am I paid exempt salary. At this point my job is in jeopardy.

How can I communicate clearly this limitation?

Is there anyway to address this without outing my coworker for time theft? Should I out her or does that look like an excuse?