I think you are with well within your right to list it on Ebay. It has been over 10 days, they are reading your PM's and not responding, and no MO has showed up in your mailbox. So I would basically assume they are not interested. I would have personally done the same as you did.
I would maybe though send her a PM that states the item is up on Ebay now and she is more than welcome to purchase it there. But as for now the agreement is off between the two of you.
Because she obviously couldn't follow through.