Send a letter CRR to the tenant giving them the option of appearing with you and the locksmith to change the locks. Inform the tenant per your states LL/T laws, they are REQUIRED to provide you with a key, even quote the statute.
It would be nice if you would inform them that this first initial lock change will be of no charge to her, BUT if she continues to change the locks, you will be forced to call a locksmith and charge her for all associated fees each time you are required to change the locks.
"Alaska landlord" has been banned, now, FOUR times for providing inaccurate and false advice. ALL of AL's posts should be taken at face value and heavily verified by a competent Real Estate Attorney.
RIP JETx - Your terseness is sorely missed...