Okay, you have convinced me... Keep them as-is.

I'll have them re-sized to the same for her (size 7). Further down the line if she wants something matching of her own we can do that. The agreement will be that if we have a kid, they gets passed on. If we break up, I get them back :)

My opinion if you want a true surprise is to find one good stone and put it in a simple Tiffany setting (the jeweler should through one in for free.) Then she can have the stone set in what she wants when the time comes.