I’m very sorry to hear this. Sadly your bird is much too young to be with another bird, and this made her try to lay eggs at too young of an age. It sounds like she might be egg bound or suffered an injury from laying the egg. Egg binding is fatal if she can’t push the egg out. Her best chance is for a Vet to try to help her. At 6 months old, she is not physically ready to lay eggs. Cockatiels should not be put together as a pair until they are both 2 years old. This is not to lecture you or make you feel bad, but to help you not to make the same mistake again. If she survives, you need to separate her from the male and do not place them back together until both birds are 2 years old. This gives both birds the time they need to finish developing physically and emotionally. I do hope you were able to find help for the female.
Thank you for asking Lafeber,