My pet dog (female, 3.5 months) Jenny died few hours ago due to some knot in the stomach, is that possible?

It sounds like bloat which is very sad and painful but it does happen. Some dogs are more prone than others. I understand your grief and I'm truely sorry that you lost Jenny. It is perfectly fine to be sad, angry, upset and frustrated. I know you feel like punching god in the face but that won't fix how you feel. Time is what you need to accept and deal with your grief. If a necropsy is performed you could see if maybe something she ate caused her stomach to knot and her to p on. In time you will heal and maybe one day after you grieve and have time to heal a new pet will come into your life and will give you the companionship Jenny did. I would wait until you can have a pet with you wherever you are beforehand. Again I am very sorry you lost her at such a young age and I hope that when you let out how you feel talk or write and just get it out. If you need to cry do it. I know you are upset but don't try to hurt yourself in a way to express your pain. I hope that in time you heal and the world returns to normal and you can find a new pet to share your life with and it brings you joy and is with you for many years.