Wow! That's a huge amount!!! I can imagine your excitement!!! I would give it to her, her total being exactly $3,000 (WOW) for $100 less than that. It might seem like a lot, but with that huge of an order, I think you cold afford to help her out a little!
I would DEFINATELY make her purchase AND PAY before you start to make those 120 necklaces!
I would put in a huge thank you note, handwritten, so it's ore thankful seeming and personal(: IMHO