What if she hates it?

I'm usually very nervous when I share my writing with someone, for many of the same reason's you've mentioned. For the most part, I've found that most of my worries are unfounded. As long as your a compitent writer you shouldn't have to worry to much about them thinking it's trash. They may have some critacisms, but so long as they aren't mean, try to take them as constructive suggestions. After all, why do you want someone else to read it except to see how you did? If they like it great. But if they like some parts and not others, even better. Then you know where you did well, and where you did not. Take note on that, and use it to improve your writing further. That's how you get better.
As for worrying about them thinking the characters are them, that kind of depends on whether the character is or not. If the character is not based on your crush, i highly doubt this will be an issue. Most people don't go looking for themselves in other peoples writings. If you did base a character on your crush, it may or may not be noticable, depending on how close the character is to the original. If you based them loosely on your crush, maybe using thier sense of humer as inspiration but changing most of the rest, then I doubt it will be an issue. Even if it is s more close match, I kind of doubt they will notice. Our perception of ourselves is often pretty different from other peoples perception of us. Since your character would be based on your perception of your crush, and not thier perception of themselves, they likely wouldn't notice, since the two are not the same. The only way I could really see this as an issue, is if you litteraly just put them, using thier discription and name, into the story. They would probably notice that.
Basically, I would say do it. Getting constructive critacism is good for your writing, use it as a way to grow. I think a lot of your fears are likely unfounded. So let your crush read it. I hope they like it.

 

I would recomend not changing things now. Go through, check for minor things like tense shifts, spelling or punctuation errors, and stuff like that, but don't change the plot or anything. That is a slippery slope. You change one detail, and suddely you have to rewrite the whole thing. You don't need that kind of stress, not now.
One thing to keep in mind with writing, and really any form of art, is that we are sometimes more critical of ourselves then our readers are. We made the thing, we know what it is supposed to be, so we can see any little flaws. Your reader does not know what you intended, or meant it to be, so they can't see the little mistakes. Unless they are specifically trying to be critical, they will likely not be as harsh as you are.
If you want feadback, and feel confident sharing with an internet stranger, I'd be happy to read a excert and give you some feedback. I'm no expert, more a casual hobbyest. But I did take some creative writing classes in college, where I read through and edited my classmates work. Not saying you have to, mind, just saying that I could if that might help put your mind at ease.
Anyway good luck, hope things go well.