Playing multiple service accounts on same SE accountFollow

We wanted to add another FFXIV service account to our Square Enix account so my sister and I could play at the same time, but we'd still both be under the same SE account.

We pre-ordered 2 copies of the game and I was able to register my 18 digit code and link my 20 digit code to my service account, but there's not an option to create a separate service account under the same SE Account for her to enter her codes. Will it give her the option to create a new service account (on the same Square Enix account as me) if she waits and enters her 20 digit code upon first login?

Thanks!