There are a lot of variables to consider before you can consider her "prego". 1) Was she ovulating at the time of copulation. 2)If she is ovulating, are the eggs healthy. 3) Is the sperm viable. 4) After copulation was she kept at optimal conditions to better the chances of having a healthy clutch.
Not to rain on your parade, but I have seen many breedings with Atheris species that yielded no babies. Lock-up does not mean that you have babies on the way. I'm not attacking you, just maybe preparing you. Hopefully, you will see her drop some babies in six months. But don't get discouraged if she does not. Best of luck.