If something happens, I'm thinking that the "right" thing to do is drive her to the clinic, pay the D&C fee, and make sure she gets home safely.
Some people say that it is the "woman's responsibility" to be on secondary birth control, like the pill. However, the law doesn't give a flying f*** whose "responsibility" it is... In the end, if its your kid... YOU are the one paying the child support.
Shell out the $400 for the abortion. Its cheaper than child support.