Head tilts are usually an emergency, I would have her checked over by a cavy savvy vet as soon as you can. It could be anything, an infection caused by an injury from scratching herself, localised trauma/pain, e.cuniculi, sometimes mites are so itchy they can cause seizures which may also result in neuro signs such as a tilt.
What are you using to treat the mites and is what dosage? Some drugs when overdosed (such as ivermectin) can cause neurological issues, which can include head tilts. Unfortunately we can only really guess, best bet would be, as said, to have her checked by a vet.