Friends. Best friends!

My friend wants a baby. However her husband is done having them. They have three already but she is getting baby fever from everyone having babies or getting pregnant. She told me a few weeks ago that she is trying to track her ovulation and wants me to help. I want to because it would be so cool to be pregnant with my best friend. I feel as though I'm being selfish and wanting her to be but not supportive of her husband on them making the decision together. Any advise?