The answer was the same back then in 2021 too, you would have had to pay for two accounts (one for husband and daughter).
Unfortunately since then they have disabled the character transfer between Battlenet accounts.
But she would have always had to have her own account when she turned 18.
Edit: She can always play for free. There’s obviously restrictions, but you can still do a lot of WoW with just the free account option.
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