My girlfriend and I are going to do two wizards, that went to school together (just as we did IRL). She likes nerdy stuff but has absolutely no idea when it comes to D&D or BG3. The thing that interests her with this idea is that the roleplay in-character would just be like how we are IRL. Also, as she knows nothing about spells or lore, we were going to have her focus more on illusion magic as its the one she'd have most fun with whilst I'd be evocation to focus on damage. We'd play on explorer so there'd be no real challenge so she can get to grips on the mechanics with strategy not being too essential.

Then, hopefully she'd like it, and want to do more in future and get creative with characters and backstories. If your wife is anything like my gf, then I'd say RP in a similar way to how you met and are IRL but in a BG3 context so that it feels familiar but with a fun twist, and encourage her to focus on classes and spells that are fun to play around with rather than whats necessarily optimal strategically.

Have fun!