On the outside, she's just excited to basically have her own place for free.
And that's how Amy explained it to Rory when he arrived to pick her up for their dinner date in Bristol. Even if they weren't tentatively trying out this 'being together' thing, he probably would have insisted on making a special trip to celebrate anyway, she muses, glancing sideways at him as he walks next to her. Reason number two for today being a good birthday... Rory making the effort to make it special for her, saving up to take her out to a nice restaurant in the city. At least she's got one person in her life who cares enough to make an effort.
Amy had made an effort for him in return, wearing a dress that displayed a lot of leg despite the cold weather and taking extra time to curl her hair--although if she's being honest with herself, the effort was really for her benefit. She hopes, anyway. Rory asking her out had made her re-evaluate her conviction that he didn't want her that way, and she's hoping that today being a special day might earn her a really good snog. (Her hopes don't quite extend past that. They haven't even shared a real snog yet, never mind a really good one.) So she'd taken the time to look good on purpose, in the interests of enticing him. It hasn't worked yet, but then Rory has always been a shy and rather private person, so Amy isn't letting herself feel discouraged. They've still got goodnight to say at her door, after all. And successful dates are always supposed to end with snogging at someone's door.