D.K.
I would let her know right away you are in daily contact with her teacher (be in contact via email or whatever it takes) and that her lying has to stop NOW! Let her know you are very familiar with what she needs to do and all priveledges, phone, computer, outings with friends will be completely STOPPED until she has redeemed herself. Give her a few weeks to set up a pattern to earn your trust back. Explain to her, that her way of doing things is causing you to lose trust in her completely, that she will be grounded until the cycle stops and ask her how it is working for her to lie? I mean my favorite Dr Phil quote (though I don't watch him anymore) is "how is that working for you?"...it isn't working for her and she needs to deal with the consequences harshly.
Also explaining that just trust in homework will go into every day life and you will no longer be able to trust her with anything if she continues. Explaining what a priviledge to have someone trust you is, what the consequences of lying are and how it just doesn't effect her! Good luck. I would say be hard core and have her earn your trust back, if she sees you are truly talking to the teacher daily, even a sheet of what is to be done each day and you checking it off with her each evening so there is no way she can lie may help!
HUGS