I'm not sure if how long she has been playing matters or not. I think that if she knows the rules and feels comfortable being the lead in everything , she can DM. Still, you can start something small to get your feet wet like some of the DMsGuild free or PWYW adventures. She may hate being the DM and waste 30$ on a larger adventure. You can also take the free part of the elemental evil arc and skip the town part, starting at one of the dungeon sites- handwave the town part and just say you were sent here.