Couple of items.
Be careful when you say "she wants me to stay in america" I realize you also said because she loves you, but if you say this it can give the appearance that the marriage is only for the purpose of staying in the US.
When you go through the process of the I130 & I485 you will have to provide evidence that your relationship is legitimate and that you have a life together. Some of those items include employment record, tax filings, current living address/situation. The more of this type of evidence and other things, the better it will be when evaluated by the ICE.
Because of your age and cirumstances, you will be in short supply of of these types of evidence. You will need to be able to explain the situation clearly and as detailed as possible. Being full time student will explain the lack of employement, and also the fact that you do not live in the same place. This will be suspicious, but as long as you are clear, it should not be a disqualifying issue.
Regarding taxes, if she has not filed for taxes on her own, there is a good chance her parents claimed her as a dependant. I am not sure, but it might be of help if you submit her parents tax returns where it show that she was listed as a dependant.
One other factor that will relate to the Jobs, is that someone will have to sign an affidavit of support for you, indicating they will take on the financial responsibilty for you, so you do not use public funds (ie, welfare). If you and your girlfriend are not employed, then you probably will not meet the financial requirments necessary, and someone else will have to take on that responsibility. That is a big commitment.
You are in a situation where the evidence is not strong. They simply cannot take your word that this is legitimate. It would be very beneficial to speak to a lawyer directly so they can go over all the info and help you out step by step.

