Help with coworker problem?

I have a problem with a coworker. She has been leaving hours early from our 12 hour shift. She does not tell me she is leaving not does she ask permission to leave. For some reason I get stuck with her job once I figure out she has left. It is not an option to not do her work either. She is a triage ma and is the one who gets patients, takes vitals, fills out all the information in the electronic chart. No one will help me do her job. I am a rad. Tech and take X-rays ct scans, bone scans. So while I am doing my job I end up doing hers too. It makes me so mad and frustrated. She also tells lies to the supervisor about me, it never pans out. She acts likes best friend one day, and the next she is bashing me. What do I do?