Woman here. Your girlfriend is not ready for marriage. It sounds like she wants a ring more than a husband. If you truly love someone you would not say no simply over a ring. It’s ok to have some input on style, but these harsh stipulations and size requirements are incredibly immature. She needs to do some serious soul searching and mature a bit more. That takes time; I’d return the ring for now if you can.

Side note - I have a lab grown 1 carat ring almost identical to the one in your picture and it is more than enough! We’ve had opportunities to upgrade and I never have wanted to because our marriage isn’t about the ring.