Should I "tattle?"?

I work in a very small office with only a few people and virtually no direct supervision. Our immediate superviser is in a different building and never comes over here.

One of my coworkers has taken more and more liberties with this over the years. Her contract here is supposedly ending in a few months (although it has been extended multiple times) so she has been job hunting and recently got a part-time job.

She has always been pretty lax about showing up to work, but since the part-time job she has started lying about it. She will tell the rest of us that she has a “doctor’s appointment” when in fact she’s going to her other job—and we know this because SHE POSTS ABOUT IT ON FACEBOOK!

For years, we have ignored her absences and not said anything to our superviser. But I think her lying to us is the last straw—especially because she asks us to pass on the lie to our superviser, sometimes. None of us are willing to lie for her.

Should we tell our superviser what she is doing? Or just wait for her contract to run out, and hope it is not renewed this time?