Primal for iOS. It's easier for normies because of the built in wallet for zaps.
Primal or Amethyst for Android. Amethyst is more stable and feature rich, but if you go that route you'll have to help her set up the Alby browser extension in a PC browser and help her set up NWC to Alby in Amethyst.
For buying and taking custody of small amounts of Bitcoin (buys of less than $1k) I recommend buying on Strike and withdrawing to Phoenix wallet. See below 👇