I agree with Marsha that IF the counter-offer you gave was a match to what the bank gave you (ie: they countered at $200K and you came back with $200k), it should not be too much longer for them to formally approve the short sale. I rarely see the bank dis-approve the when the counter-offer they make is matched by the buyer.
However, if they countered at $200K and you came back at $190K, they will go through the entire review process again. This still should not take more than 30 days.
Bear in mind though, at 4 months into it already, the process is coming very close to the 6 month limit the banks have. Once 6 months is up, the seller will have to provide updated financial information to the bank, and the bank will often order another appriasal, as the market value may have changed within the 6 months. This can significantly delay the process again.
Short sales are NOT short, nor are they easy. They are often frustrating, exasperating, and time consuming. Again, I hope your agent AND the sellers agent are aware of these parameters, and are familiar with the short sale process, or else you could be waiting a long time again for the approval.