How do you deal with lying friends?

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One of my best Internet friends was always talking about her baby. I'd never met her in person, but we talked constantly by email. She'd always made herself out to be a new first time mom. And, then later, I found a post on another message board where she talked about her 13 year old son. It kind of creeped me out that she hadn't shared the fact that she had another kid. We shared everything! We talked about everything! You would think something like an extra kid would have come up in the conversation. But, she never mentioned anyone but her baby. And, it made me wonder why she'd hide an important fact like that. She didn't seem to mind talking about her baby, so why not mention her older son? After that, our friendship sort of dissolved. I think it was just a pattern of her deceptions and not the first lie that broke up the friendship. It was hard talking to her after I found out she was hiding stuff. I wanted to ask her about her other son and why she hadn't told me, but I was afraid to do so. Not that I would expect a friend to reveal intimate details of her life to me. But, she didn't seem to mind sharing everything else, why was it so important to hide one little fact like an extra kid? It made me wonder if she were really the person she claimed to be or if she had other intentions. How do you deal with a friend that lies to you constantly or hides stuff about themselves?