Yes

My wife and I are talking her status. I came here at 2003 with H1B visa, my wife came to US in H4 which is not allowed to work, but she changed her visa from H4 to H1B two and half years later. My H1B will expire in one year (at that time, my H1B will be 6 full years), but the first three years of my wife's H1B will be used out in about 10 months. This means, when my H1B expires, her H1B will alread end before that. My question is, could my wife extend her H1B for another three years, if yes, this should mean that her status has nothing to do with mine, and I might be able to change my status from H1B to H4 to be a dependent of my wife and we can stay in US longer, is this right?

Yes