With that clarification, you need to contact the state DMV and let them know that someone has fraudulently used your name and address in an auto registration. Depending on state laws, that is often a felony.
If she has used it for a P.O. Box, contact the box owner and let them know of the fraudulent use also.
With her doing that, it is obvious that you should get copies of all three credit files and review them for improper accounts and access. You might also consider contacting all three Credit Reporting Agencies and asking them to put a "Fraud Alert" in your files.