I only just saw this thread but, phew, good to see so many other gals are on it!
Cut matters A LOT. I want the best cut for my earrings precisely because they aren't looked at as closely - badly cut diamonds aren't going to have any presence nestled back there on the ears and what a colossol waste of money. On the flip side, clarity and colour is where you can compromise with earrings for sure, like others have said, providing you've maximised cut. A Hearts and Arrows diamond is the creme de la creme of the round cut. You'll find come across that term with a bit of research.
Read up on pricescope.com forums. Good Old Gold also has some really good starter info in easy to understand language:
http://www.goodoldgold.com/4Cs/
I don't believe that she mistook cut for shape either. The shape is
round! I think you could safely assume she's bumped the colour and clarity grades up without the restriction of certification: you can't see inclusions in a true SI dimaond with the naked eye. She does sound like she's trying to take advantage. Incidentally, I was looking to buy a stone cut in-house by Good Old Gold (not yet certified) and they gave me the option of GIA certification before purchase... at zero cost to me. That's the way it should be. 15% - 20% more? She's just making sure you don't get them certified, because it'll disprove the stats she gave you. (Also, AGS and GIA are generally considered the best - i.e. strictest - certifiers.)
This actually makes me very angry. She's your Mum's friend so I'll leave it at that. You'll be spending a lot of money to commerate a whoooole lot of hard work: take your time to put in a bit of research and you'll be so thankful you did. The stones you see in Zales have got nothing on a super ideal cut stunner, not to mention are very over priced for what they are.
Last but not least, congratulations! What an achievement.

Ask as many questions as you like.