Assuming that things went down exactly as you told them (I am usually wary of hearing stories from one side) there are a few things I am wondering.
1- What is her motivation for not wanting to adopt/abort. If this was truly a terrible accident, in which case the pill thing sounds sketchy, girls are typically MORE vigilant when they're sexually active, why doesn't she want an abortion/adoption? Parental pressure/religion/social pressure? Or did she want to get pregnant? It would help to know how old you are, is this girl 16 or 30?
2- What was going through each of your heads when this happened, you liked her, we established that (and we promised we won't berate on the quality of decisions) but what was her motivation? One night stand? Making your friend jealous? Genuine interest?
3- Do you honestly think she intended for this to happen or is it a way of justifying the outcome and passing off some blame for a bad situation? The pill forgetting thing does sound dodgy I admit.
If she does give birth, you really have two main options,
a) Get together for the baby's sake, I definitely do not recommend this.
b) Pick up an extra job and pay child support, and forget it ever happened. This option will mean you have less free time but in a few years down the track, will probably not affect you too badly other than being slightly poorer. If you cannot convince her to adopt it out, then there's not much you can do, involving yourself emotionally will probably just cause all sorts of heart ache in the long run, this includes seeing the baby or taking on a pseudo fatherly role. I suggest, failing to convince her to adopt, you should have a good long discussion with her about what you both want out of this, it is unrealistic of her to expect you to become a loving father after a one night stand, especially since its HER decision to keep it, but you need to take some responsibility if it is in fact half yours (make sure you get a paternity test just in case) and pay child support.
You never know, you might strike it lucky and she will miscarry...