Mini dilemna-need advice on this

Ok I have a mini dilemna I need opinions on...

I purchased something from an EBay seller. They listed the item price and the shipping. I think ok not bad so I bid. I won the item. So I get an email from the shipper telling me that she has sent the item (YAY!) but that she never went to the post office beforehand to find out how much it would be, so turned out to be 5 bucks more than she anticipated. She wants to know if I can send her the extra 5 bucks even though she cannot 'hold me to it.'

Now I feel torn. Yes it is 'only' five bucks, but it is a 5 bucks that would have made me decide NOT to buy that particular item because there were similar items liisted that would have been less had I known from getgo she intended to charge me 5 bucks more.

So I feel bad for her but honestly, if you are a seller on ebay you know the drill; you go to the post office BEFORE to know EXACTLY how much you are going to charge or you write 'shipping to be decided' so the buyer knows what they are getting into.

I guess what bugs me the most is she could have emailed me BEFORE she shipped it; like said 'Hey Im sorry but shipping turned out to be more than I said and it would be whatever. Are you still interested in the item or do you want to cancel the transaction?' I could have had a real choice then. But now its sorta like Im being backed in the corner by the idea that I 'should be the nice one' when its not MY fault.

So my question is should I send the 5 bucks even though she was a bit A) lazy with finding out the shipping costs and B) Has put me in an awkward spot. Or should she be the one to use this as a learning experience?