Erik Said:

How do I deal with this?

We Answered:

I do feel your plight. Her academic achievements reflect on you, and she is uninterested in learning the material needed to pass her tests.

Only speak to her in English going forward; it will help her in the long run. She feels as if she is able to slack and go back to her comfort zone with you. That is a cycle you need to break. When she asks you a question in Spanish, calmly say, "In English please" and work from there. I taught English abroad, and when my students didn't understand a concept, I would simplify the speech, draw pictures, or act it out, not switch to their native tongue.

Only help her on YOUR terms, not hers. You need to assert your authority with her, or she will continue to do whatever she wants.

Buena suerte!