Yes, absolutely it's possible to fall in love with somebody through the Internet. Look around you at all the significant friendships that have formed on this board and throughout the Internet. If you can refer to a whole board as "family" which many people do, then heck yes, you can fall in love with somebody through the words they write.
People tend to be WAY more open and honest when they are talking to somebody they don't see, and that can explain why your friend has come to feel so close to somebody she just "met." Pretenses fade away when you don't have to worry about what the person at the other end of the computer connection will think of you which brings about a level of truth an honesty that most people don't engage in with their "real life" friends or partners. Many people are afraid to reveal their real selves to the people in their lives. Then they go on the net and open up to a stranger...many times they open up in ways they never had in their entire lives. When the person at the other end still likes them, even though they've shown so much of their true selves, it can be intriguing and encouraging...and these relationships tend to move quickly.
I met my partner on a message board four years ago...and I've never been happier in my life. There have been dozens, perhaps hundreds of couples brought together through the same message board. The vast majority of those couples are still together.
What I think is wrong with the situation with your friend is that she is developing a relationship with somebody while they are both married. I feel very strongly that one should never begin a relationship with a new person while "with" somebody else. If she's not happy, fine, divorce or leave the person. If she loved him enough to marry him, even if she no longer loves him, she owes it to him to let him go before moving on. Another thing, I'm a firm believer in taking some healing and/or self-reflection time when one relationship ends before starting a new one. I've worked with a lot of dysfunctional people, and I swear, it seems to me that the most grave mistake people make is that they refuse to like themselves enough to spend time alone. People rarely believe this, but they NEED time after a relationship before entering a new one. Most people lose some of their identity when in a long term relationship, even if the relationship is healthy. A sensible person will spend some time getting to know their own selves before trying to show who they are to a new person.
Anyway, when I met my partner, I had been out of an abusive relationship for about 16 months. I still wasn't ready to date, and this person understood that and we backed off for a few months. I knew I liked this person, but I also knew that I didn't want to bring past issues into a new relationship. I went through some counselling and several months later, we reconnected and are now living happily ever after. Tell your friend if it's really love, it can wait until she takes care of her current issues in an honorable way. Only after she's dealt with her baggage will she be able to be an equal partner in a new love relationship.
I hope you know what I"m talking about. I just wanted to give some insight on my friend. I do love her to death, but she is a little out there.
) She moved to Australia and they now have a baby daughter. They talked to each other for about a year before they actually met. He came over here for a couple of weeks. Then they commuted back and forth for about 2 years before they married (long commute). 
