I teach a class with a very high proportion of ELLs. Brixton's post is spot-on. I am truly ashamed of what our administrators have done.
The only thing I'd like to add is that this student, as you describe her, is not making even minimal effort. She is not contacting you to say she does not understand your comments, or to argue that she didn't plagiarize, etc. Her failure to change in respond to your comments suggests that she doesn't even read them. She is not even making the basic argumentative grade-grubbing effort. And you have no way of knowing why: is the student depressed and needs a level of help that professors are not trained to give? Is the student out with a boyfriend or out partying, having a great time, hasn't bothered to check her grades and doesn't care? Or, has the student paid another ELL to take the class for her (yes, this is more common than you would believe: an ELL asking another with less bad English to write a paper).
Regardless of the true situation, giving a passing grade for the level of effort and mastery you describe will not benefit the student. An F (or an accumulation of Fs) will necessitate a change of course, and a change of course might benefit the student, whether it is hitting rock bottom and seeking help for depression, or a wakeup call to stop the partying and start working, or to find a better ghostwriter.
It doesn't sound like your institution will give this student appropriate support, but that would also be a direction to try.