Interesting. We never saw any sign of cannibalism. Only thing we do is feeding of both animals beofre placing together. We keep male with female several weeks in one cage easy, after it just change female for another one. Our cages are built in the way we can fee both animals in cage at the same time, 1 in hidding box, second in terrarium. So we keep them not very hungry all the time...
We have also second male, which is small probably as your female, but we use him just for mating with smallest female. Previous owner of him didn`t care much about his feeding during growing, so he is quite small....
Females of Naja naja need to be older to start breeding, in our experience approx. 5 years old. We tried it sooner as well, but it didn`t work...