I was hit in a parking lot by a co worker and they do not want to take responsibility, what do i do?

What you "should" do is not something we can advise you about, since that depends on your tolerance for stress and conflict, your need for additional compensation, and the degree to which you feel this is unjust and that you need to do something about it, even at a (potential) cost.
What you *can* do is sue her--her personally; the employer is not liable--if you think that she was more than 50% at fault (but see below) for costs or losses you incur in excess of anything you receive from insurance (e.g. for your deductible; for that amount of money, suing in small claims court, as your own attorney or "pro se," makes sense).  That would be the only way to compel her to pay more. But obviously, suing her will not help your relationship with her and can hurt you at work; only you can decide if that is worth the chance--not the guaranty; only the chance--of winning the amount of money at stake.
Note that in my experience, both as an attorney as someone recently involved in a very similar accident in a store parking lot, is that when you are both backing up, a 50-50 apportionment of fault is common. It is not impossible to overturn that and show that she is more at fault, but it is unlikely; your chance of winning is not necessarily good.
Another thing to consider: unless you have a written employment protecting you, you are an "employee at will" and you manager can make your life as miserable as she wants, and can even terminate you (if upper management lets her) at any time, for any reason, or even no reason at all. If it looks like she will not be leaving this job anytime soon, you may wish to start looking for a different job.