I presume you are saying you had one hen die from the worming process.
That is why I use Warzine first, followed two weeks later by Ivermectin. Warzine kills some worms first and helps lighten the load for the girls. Whereas Ivermectin, by itself, kills all of them at once. Thus, on occasion, the die off and expelling of the dead material proves too toxic (fatal) to the bird. Thus the safer way is Warzine first followed by Ivermectin 2 weeks later. Then people can eat the eggs 2 weeks after that.
There is an opinion that if one regularly worms (6-9 months as I recall), then Ivermectin alone should not be too hard on the birds.
I found that we are able to have 4 weeks of eggs in the fridge without any problem before beginning the process so no loss of eggs for the family. We also found that the girls consistently increase their weight and really show improved health/activity with the eggs being fed right back to them. We can see the difference within the first week.