For a sarcastic exclamation in American English that fits the tone of the scenario, a good choice might be:
- **"Oh, so glamorous!"**
- **"Wow, so fancy!"**
- **"Yeah, real classy!"**
- **"Sure, like a millionaire!"**
- **"Oh, so posh!"**
These phrases carry a sarcastic tone, especially when paired with the right vocal emphasis. They would work well in the context where the girl disagrees with being described as looking "fancy" or "rich" and instead mocks the idea.
If you want something more colloquial or playful, you could also consider:
- **"Yeah, totally red-carpet ready!"**
- **"Oh, I’m just dripping in luxury!"**
- **"Yeah, like a real heiress!"**
The key is in the delivery—tone and body language would emphasize the sarcasm.