When the crown is pulled to position 2, it will “hack” ie stop the running seconds. Perhaps when you reinstalled the stem, you did not engage the mechanism properly, preventing the watch from running. Try reinstalling it, but now you run the risk of further damage.
I suggest you you get the watch to an authorized IWC Service Centre.
At this stage of proceedings you need to go to an official IWC repair center so that you can get the watch repaired correctly now and make your mother happy again.