2 Accounts, 1 PS4

Hello, I have a general technical question!
My wife and I both play the game. I play on PC, and she plays on PS4 through my PSN account. My question is that I'd like to also add service for the PS4 to my account that has my PC character. I don't know what to do, because when I open FFXIV on the PS4, it doesn't give me an option to put in my SE ID.

Do I have to re-buy the game on PS4 to be able to log my PC account into it? And if I do, will there even be 2 FFXIV able to be on the cross media bar on PS4 home screen?
Or is each FFXIV restricted to 1 PSN account?

If anyone can help me figure this out so that my wife and I can play on the same PSN account, but at separate times (because I want to use my PC character on PS4 when she's gone) it'd be greatly appreciated.

Only one PSN account linked per SE account. If you want to play on PS4 using your PC account you need to buy another PS4 copy of the game, create another PSN account and link the new PSN account to your SE account.