Well, this is fairly easy to determine its worth.
Apple is selling refurbished MBAs with a full ONE YEAR WARRANTY. In addition, these MBAs are "like new." They always repair any damage completely and then essentially insure it by guaranteeing it for a year. In addition, you can extend the warranty to three years by buying AppleCare on eBay for around $110.
The problem, most likely she is not going to like the price. She paid a small fortune for that MBA, and it is just not worth it since Apple is clearing out there MBAs for so little.
Original MBA refurbished pricing:
1.8 GHz with 80 GB HDD = $1099
1.8 GHz with 64 GB SSD = $1299
I would advise you to use this as a pricing guideline and reduce the price for hers from this price. Remember this is for a like new system with absolutely no damage that Apple is guaranteeing for a year to three. Hers will most likely not include a one-year warranty.
To see those prices, go to Apple.com. Click on "Store" at the top. Scroll down to near bottom of page. On left side, will see a link for "Refurbished Mac." Select that and you will see all of the refurbished MBAs. Also, sometimes the 1.8 GHz with HDD is not listed, wait a few days and will see it again.
If it is a 1.8 GHz with SSD, she may have paid $3099 for it... be very careful to not make her "Mad" by showing her the prices on Apple.com. Most likely, she will have no clue that the value has dropped so very much... $1800 in eight months since when Apple reduced the price to $2499 and then to $1299 after stopped selling that model.
Basically, Apple came out with a revised MBA that is 1.6 and 1.86 GHz. It has 120 GB HDD or 128 GB SSD. If her MBA is one of those, the pricing is much higher. But, I assume it is not since you listed it as a 1.8 GHz which the new model does not come in - it's a 1.86 GHz. Also you said it's six months old, the new ones were released four months ago.
Best wishes with it. I hope she knows about the price drop before you discuss it with her.
