Yes, good tip about trying your best to find out her ring size (friends, other rings she has but maybe doesn't wear often you could "borrow" from her jewellery box).
It's a bit of a downer when you want to tell people you're engaged and your brand new ring is in the jewellery store getting re-sized. Happened to me and also one of my friends recently. Definitely one of the first questions women friends ask when you tell them the engagement news is "let's see the ring!!". So if she doesn't have it on, it takes some of the fun out of it for everybody.
Edited to add: There are lots of stores in Calgary that will give you the GIA/AGA certification with your ring. Troye Shoppe, Calgary Jewellery, Birks... just to name a few that I know do for sure. Also none of these stores sell conflict diamonds. Most mall jewellery stores also do not sell conflict diamonds (they call it 'The Kimberly Accord' I think).