What is the wife's liability?

I had several years of unpaid taxes (2004 - 2011) that I recently filed all together. I was advise by the agent who prepared the taxes to pay all of the taxes for everything due all at once and wait for the IRS to respond before settling the penalties and fees, and did. For 3 months I heard nothing back from the IRS until last October I received a letter stating I still owed $150.77 worth of penalties and fees for 2011. Nothing else about any of the previously unfiled returns. I wrote a check that day and put it in the mail. I tried calling the IRS several times between then through the turn of the year but met a message each time saying they weren't taking calls due to all the new tax laws. In December my wife and I visited another tax agent to help us refill our 2011 returns as married to try and claim some money left out there. We got a letter back a few months later in March saying we were owed an extra $949 and to expect a check in the mail in a couple weeks. One week later we got another letter saying we would be refunded $0 due to all of it being applied to taxes I still owed from 2010. Still receiving nothing else from the IRS and not being able to get a hold of a live person, we went into HR Block. They helped us file our 2012 taxes and were able to get me in touch with a live person at the IRS. They informed me there on the phone that I still owed $924.49 for 2007, $3877.34 for 2008, and $401.10 for 2010, totaling $5202.93, and that I have already been passed on to their collections department. Unfortunately we learned while there that for 2012 we owe $2309 to the Fed and $1108 to the state. My wife and I have been married since 2008 and she has been filing her taxes (married separate) all along, all of the past debt is under my social security number. Not until recently refilling our 2011 return (and our soon to be filed 2012 return) have we filed anything together.