This look is not a look of happiness. This girl just got engaged. Apparently the easiest decision someone should make. She’s looking at the ring, convincing herself that this is right, that Finn is what she wants. At this moment she probably has what Quinn said going through her mind, about her having an amazing life, but at this point, all she thinks she has is Finn. That is the only reason she said yes, and I honestly don’t understand how people think she’s happy about this.
Also, this is not the face of someone who thinks they made the right decision: