I’m very sorry you are going through this.
Even though that coop is a large prefab, I don’t know for sure it is big enough for 14 hens. The ventilation worries me unless you added more when you set it up, especially if it has been upwards around 100 degrees, coupled with the stress and hormone surge that comes with being a new layer. Have you made any modifications to the coop to help with air flow? There are some members on here that have made amazing modifications to improve the durability of coops like yours and improve breathing conditions for the chickens inside. Hopefully someone can comment with some suggestions.