Well, she states she wanted children but was unable to have them.
It is possible she had PCOS. Although, she never looked like she had a weight problem that often happens with it. Nowadays there are better ways to deal with PCOS.
My quick read of her wikipedia entry said she didn't want to have children with Brad Pitt. She was in her 20s.
My first thought was "There was your opportunity, and for some reason you decided to blow it."
While there might be better men out there than Brad Pitt, I don't see how most women wouldn't consider him at or near the very top of desirable mates.
I feel sorry for her. I feel that children provide a sense of purpose and a source of love, and I am sorry she missed it.
For many people it is not so easy to have children, and I hope she didn't miss out simply because she dilly dallied and missed her opportunity.