Making a google account for someone with no mobile number

On a computer the phone number step is usually optional, there's a Skip under it. It's when Google's systems get suspicious (lots of accounts made from the same network, a VPN, etc) that it insists. If it won't let you skip, use your own mobile to verify, then go into her account settings afterwards and remove your number. Add a recovery email instead, yours is fine, so she can still get back in if she forgets the password. Don't bother trying the landline, I've never had verification codes work reliably on one.