Beware of spoilers in the latter part!

So, here we go. Apart from stalking a boy named Natsuno Yuuki and dreaming about being his girlfriend, Megumi is your average teenager who's keen on eccentric fashion and big city life. She hates her village and wants to get out of there. And here are some slight differences between the song's heroine and Megumi:
"...Wanted to belong here
But something felt so wrong here..."
But something felt so wrong here..."
No, definitely not. I've never seen a scene where Megumi said something like this. It's the opposite: she always pointed how much she hated the village and it's inhabitants (especially for not having any interest in the outside world). So just the second line is true about our heroine.
"...Buildings with a hundred floors
Swinging around revolving doors..."
Wearing strange, eccentric and too colorful clothes? Wanting to be seen, becoming an idol for other teenagers like her? That's our Megumi - normal girl with an oridinary dreams? Fashion, fame and flashy things? Maybe a little too shallow and material? Who can you see? A little bit naive but strong-willed girl that is too young to undestand the new responisibilities and obstacles waiting for her if she tried to "breakaway" or selfish and shallow girl thinking only about herself and not even trying to imagine the consequences of her action? I guess that's both. All in all, Megumi's just a teenager - not a child anymore, but still a having a long way to become an adult. Still having sometimes stupid and naive dreams without any real life experience.
"...Out of the darkness and into the sun..."
Then... Which is it? Things become rather complicated when Kirishiki family moves to Kanemasa mansion in Sotoba. Megumi starts daydreaming about a noble family that came from a far away (presumably some big city) and is interested in her. Well... They later become interested in her but for "slightly" different reason. And so, here the darkness starts - shiny and sparkly Megumi is consumed by the shadows, dies and later becomes an undead vampire killing others villagers with disturbing pleasure, even her friends relatives. Did she really become so cruel or was it the only way fo her to exist after having her dreams destroyed? How much frustration did she hide? The viewers could see only her bestiality and hunger for blood. How much of that was her vampire instinct and how much her own nature? I guess she adapted to the new condition and survived pretty well casting away her conscience and dreams. Seeking redemption? No, I think she wasn't (yes, wasn't) that type of person. She never really came back to the "sunny" side (not that she had a chance to...).
"...I'll spread my wings and I'll learn how to fly
I'll do what it takes til' I touch the sky
And I'll make a wish
Take a chance
Make a change
And breakaway..."
"So much for my happy ending" is what the story wants to say. Being changed she enjoyed her full rights of the vampire. Later took advantage of the chaos and tried to escape by herself revealing that she still wanted to go to the big city. But whole novel/anime getting a rather downer ending resulted in almost every character going downward. So, Megumi is one of those sad examples having their dreams bitterly crushed (literally - by a certain tractor and a stake) by the fate. Her breakaway was almost impossible from the beginning and her dream was actually a small and unimportant detail in the ocean of all troubles presented in the story.
Well, I guess that analogy was pretty obvious and easy to analyse, but everyone has their beginning and it's just for fun as I mentioned above. See you! :)