That's definitely one way. Giving her an Arrival Sensor would work, but you still have the timing issue if you are going to try and Disarm and Unlock the Door using a single Routine.
Without getting overly complex if you were to go that route and give her a Physical Arrival Sensor, I would create two routines.
1) When her Arrival Sensor is Present and system is in whatever Armed State, Disarm SHM, and set the Mode (create a custom mode called her name or something) and set the system to that.
2) 2nd routine, when her Arrival Sensor is Present and the Mode is "her name", unlock the door.
Just a thought. You can also do something like this without giving her an Arrival Sensor. The Echosistant @SBDOBRESCU @bamarayne App has a Device Handler that allows you to add a Virtual Presence Device that you can within ST set to Present or Not Present simply by clicking on it so you can still keep control of your system without giving her anything. You would have the same routines above and when she says she is at your place, you can click on the virtual device to Present and the routines will fire. I'm only giving you some very basic ideas without having to put a whole lot of time and energy in, because there are more complex and powerful ways to execute some of these things with some other SmartApps that are available.