Legal Question in Real Estate Law in California

No, a lien can only be placed upon property owned by the judgment debtor. As a girlfriend, as opposed to a wife, she has absolutely no community property ownership rights as to anything you own. If the creditor has her address, you might want to send them a letter stating that you ae not married to her, the property is soley yours, and if they attempt to place a lien on it you will sue for their creating a cloud on title. Some reasonable attorneys would advise against contacting the creditor so as not to alert them to the existence of your house, so my advice is not 100% certain.

Unless you are registered domestic partners (or married), neither you nor your property is subject to lien, garnishment, seizure, etc. for the debts of a live-in girl friend.

Since you share an address, there is a moderate possibility that you might get debt-collection attempts against you (letters, phone calls) and a strong possibility that she will get some at your joint address. However, unless you receive something that is other than a mass-produced collection letter, and makes obvious direct and personalized threats of collection efforts against you or your property, I'd ignore the ones addressed to you.

Do not ignore anything resembling a complaint, summons, notice of levy, etc. that looks individualized or is from a lawyer, sheriff or court.