Magdalena Larkin (played by Belita Moreno) is Theresa Russo's (née Larkin) mortal mother; Justin, Alex and Max's maternal grandmother, as well as Jerry's mother-in-law. She only appeared in the episode Quinceañera to attend Alex's 15th birthday party. Justin and Max are very close to her because they like to wrestle with her, especially with Gandma always winning. She is portrayed as a very cool grandmother.
Since Magdlena is Theresa's mom and not Jerry's, she doesn't know about the existence of magic and wizards, so the family had to reduce the use of magic when she visited for Alex's birthday. However, Alex disobeys her parents and uses magic to switch bodies with Theresa so she could have the Quinceañera she always dreamed of when she was 15, despite she was caught by Justin and Max.