Three things.
1)
Is it odd that I want the ring back?
A more pertinent question might be, “why do you want it back?” (And also, why does she want to keep it?)
2)
Personally, irrespective of “now” the way I’d look at stuff like engagement rings is the same as any personal history; it’s a product of its time. If I gave someone a ring it was to express how I felt at that time, how I might feel now doesn’t change how I felt about them then, and it would be a disservice to the past few years to demand it back. What the hell would I do with it anyway, pawn it for a tenth of its value?
If roles were reversed I’d expect to keep any gifts, unless they were personal to the giver and irreplaceable; eg, the ring was your deceased mother’s or something (which is a bit creepy IMHO, but just an example).
3)
You’re breaking up a seven year relationship. With respect, a (now second hand) ring is the least of your concerns. So long as she’s not taking the piss, there’s no point in being stubborn about the small stuff when you’re going to have to discuss things like custody and access of kids.