I don't blame you one bit for feeling the way you do. Heck I mourned my pg being over far too soon and they weren't even my babies to keep. It still was difficult knowing that I should have still been pg even though there were the kids looking right at me. It just felt wrong to be able to look at them stuck in a hospital instead of just being stuck in ME. Like yes, they shouldn't have been home yet, it was too soon, but basically they shouldn't have been born.
With all that said, it sounds like she is doing amazingly well and while it is a huge emotional roller coaster, there will be a day when this time seems like nothing, and you probably wont remember most of it.