The reason why she does this seems to have been more or less explained by her off-the-hand comment in the Please-Love-Anthony whingefest when she explains that for someone to be fully realized, he or she needs a house, a style and a car. What she left out is that said person also needs something else: a supporting cast. For Georgia to be more than a foil for Phil or someone to feed Elly straight lines, there would have to be Georgia people in the strip and, well, that just wasn't going to happen.
After all, for there to be Georgia people, Lynn would have to keep track of them and that would be too much like having to do a book report about a big, thick novel and that would be no fun at all. I mean, it's bad enough some people wanted there to be John people and to have John's story to be more than "big dumb immature guy with control issues who holds Elly in barely disguised contempt" when the focus was supposed to be on Elly and the kids without adding more complexity and subtracting the happiness from the process.