A lis pendens does not have a statute of limitations per se. All a lis pendens is, is a notice to the "world" (assuming it is properly recorded with the appropriate recorder's office) that there is pending litigation which could affect title of the property.
If someone has filed a Lis Pendens notice (which alerts others that there is a pending lawsuit involving a property), any party involved in the lawsuit can: Ask the court to remove the notice (e.g. Motion to Expunge). Notify all affected parties at least 20 days before the court hearing.
Only an attorney or the court can sign a lis pendens. If your attorney filed the lis pendens, then ask her to sign and record a Notice of Withdrawal of Lis Pendens. Give a copy of the title officer. You can record a certified copy of the dismissal of the case and that will extinguish a lis pendens.