Answer: Although you did not specify if the the creditor had actually filed a lawsuit against you, it is mostly likely a scare tactic. Subject to a very limited except, it is generally illegal to record an involuntary lien on another person's property without first filing lawsuit and obtaining a judgment or court order.
If the law office did send you a Notice of Involuntary Lien as a scare tactic, this is most likely a violation of the Federal Fair Debt Collection Practices Act. The law firm might be liable for damages, including emotional distress and attorney's fees.
If the law firm did obtain a judgment against you, they may have recorded an Abstract of Judgment. Recording an Abstract of Judgment does put a lien on real property in your name. Unless you are also on title to your mother's house, she should have nothing to worry about.