You might offer to meet them half way, so long as they covered your expenses. With that being said, if you COULD find a freight company to ship your two boxes, it would probably be cheaper for your client and a lot less trouble for you.
I would imagine you'd have to build a plywood crate for each chair to insure that your chairs arrived in the best condition. That's a consideration that you'd have to figure into your price. I don't really see how it could be cost effective for your client.
It's a great compliment to you that she's wanting to have you build the chairs for her.