Hi again
Even though I've had some time to think about this, I still don't know where it's going to go, so bear with me. I think we've established that we share a lot of the same feelings when dealing with others. I've never actually known what the cause is, but the result has been social anxiety.
It's great that you've stayed with college (something I wish I'd done 25 years ago and would definately change if I could). You have a chance of receiving help I never did because of money problems.
As well, I had a very difficult time describing my thoughts. I hid my depression too. For one reason or another, I was always out of reach of those who could have helped. So try to avoid this. You do have an ability to express yourself and if you just tell your story to the right person, you may be able to get a quick jump on it.
About this girl. What you may see in her is her ability to do the the types of things you wish you were able to. You mentioned spontanaity. I assume you have the same problem as I did, which is needing a lot of time to think of answers and responses. This girl portrays for you how you would like to be in ease of conversation, naturallness, clever, witty replies, and because of this she's probably popular. You study her wondering how does she do it? What is her overall attitude? She always seems to have the right response, the right timing. You think if you watch her long enough you'll find the "key" and be able to turn the lock on your own personality. You watch her movements, her speech patterns, her facial expressions. She's mystifying because you can't figure out how she does it.
The first mistake is trying to be like someone else or learn what they have that you don't. Doing this puts you in a mind frame of "they are better, I am bad". When we tell ourselves, over and over and all day and all week and all month that if we could just be like so and so, we repeat and reinforce with every thought that there is something wrong about ourselves. You'll spend hours and days and years of your life rejecting you and godifying others. It's a basic lesson of therapy that to get better with nearly any problem, you have to love yourself first. I made lists of my good qualities. When the negative thinking started, I would recite the list and feel the negativity drift away. It worked for a day or two, but I hadn't learned to tune out the thousands of ways every day I insulted myself and before long, I was back in the same rut, the list forgotten. I tried to love myself, but I went about it wrong. Loving yourself isn't just loving the good parts. It's loving all of you, including the faults. Loving is forgiving. If you can forgive yourself for not being perfect and accept the faults, and still say, I'm ok, I'm worth it, I need to get better, but I need to love myself by giving myself the time I need to grow and become the things I want to be. Sometimes we do the opposite and focus only on our faults and forget the good stuff. Then we believe we're hopeless, worthless, a mess. The right thing to do is love our whole self. Give yourself a break on the bad days, bad moments. Give yourself a mental hug cause that's when you need it most and don't try to fix it right then. Just hug yourself and say I know I messed up, I'm not perfect, I still love myself, I still want to get better, and tomorrow, the next time, sometime I won't feel this way, but right now, I'm just going to love me anyway.
When things go right, or things just aren't going bad, feel how good a person you are. Feel, I mean really feel it, how well you did just now, how that is what you want, let yourself feel how good it feels and let yourself feel it a long, long, time. Tell yourself this is what I'm going for, this is what it feels like to be the person I want to be, I did it, I can do it, it is happening, I am getting there, I'm almost there. It' really important that you reward yourself. Really, really important.
Back to the girl. She represents the you you want to be. She can be a role model, you are probably seeing her as the ideal, the ultimate of what you'd like to be. Don't try to be her, but nurture the qualities you see in her, in yourself. Is she kind? Is she honest? Does she smile? Is she friendly? Is she polite. You can be all those things. It wont make you her, but you can have those qualities of her that you so admire. You will still be you and there is no one else you can be and that is as it should be. Only you can bring to this world what you have. And you do have a lot, if you let yourself find it. It takes time. It won't happen over night. But be good to yourself and give yourself the chance.
Ok, enough for one post. My heart is with you. I hope this helps and let me know your thoughts if you'd like to.

"Our greatest glory is not in never falling, but rising every time we fall." Confucius