The timeline from locks to ovulation to laying is a lot longer than just a few days. I think you should read this...
www.ballpythons.ca/gallery/breeding.html
After you see copulations, the next step will be ovulation -- only after that has happened will she become gravid, not before. So until then, they generally keep eating (all of mine did last year). When they are gravid, they don't generally look fat or noticeable until the very very end when they brighten up and their backbone becomes prominent as their bellies descend, right before they lay. The reason for this is that they don't gain weight -- they replace body mass with egg mass, almost gram for gram. My girls last year remained at the same weight throughout the entire breeding season (maybe 2 grams difference), then when they laid their eggs, the weight of the clutch was exactly the same as the weight they had dropped. It's a very efficient process and is also why it is so taxing on the female.
Give it time, and be persistent -- she'll get there.
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~* Jen *~
Pink Lady Constrictors