It wasn't a holiday that you had planned together. She had already booked the accommodation from Friday to Friday without knowing whether or not you'd be able to go with her. She then offered for you to go for the first few days, before she started working. I certainly wouldn't have expected to pay the accommodation, as she'd already decided to book that anyway, and I certainly wouldn't have expected her to ask me to pay for it, as it was her decision! Whilst I would've been more than happy to offer to pay for one nice meal as a thank you for being invited, I certainly wouldn't have expected to pay for all of your evening meals out ... Rome isn't exactly cheap, and could easily have run up a massive bill! I think it was a downright cheek for her to even suggest it! And the issue of you having to make your own way to the airport, and have the added expense of a hotel, after she had explicitly offered for you to stay with her overnight and get taken to the airport by her husband is, quite frankly, way out of order! I'd definitely drop her an email and tell her that it's a shame your friendship has suffered due to this, but I'd have to point out all of the above details and let her know, without any uncertainty, how upset you are about the way she has treated you, and tell her you feel like she has used you, probably just because she was at a loose end for a few days. She OFFERED for you to go with her, it wasn't something you'd planned together, and she never suggested that you'd have to pay for her accommodation which she had already booked, when she asked you to go. Be open with her, and if she can't see her failings, then let it be. Friends like that are not worth having.