Start with Blockstream #Green app. Perhaps half in a single sig. wallet (that's normal compared to other wallets). The rest can go into a multi-shield wallet (multi-factor authentication).

When she's comfortable with that, buy Jade hardware wallet. Create a new wallet there (single sig) and consider sweeping all funds out of the mobile/desktop Green to the Jade, and then using the Jade's support for BIP85 to derive new keys (seed mnemonics) to re-initialize the mobile wallet(s).

This allows one to consolidate multiple wallets on one top level seed (backed up on a suitable metal mnemonic storage device. (The BIP85 derived seeds can be re-derived for any future recovery).

[Tip: you can also derive additional secrets via BIP85 — for instance to generate #NOSTR nsec/npub identities].