Is it part of a family plan contract or does she have her own contract? Verizon has an early upgrade policy. You just have to find out what date you're eligible for it. When that date comes, you should be able to upgrade early by just paying a 20 dollar fee.
Now you two have a family plan with you as the primary and her as the secondary, that's a different beast. You can upgrade your phone early, but she can't upgrade hers til Dec. I'm not sure what the manager told you, but I'm in a similar circumstance and everywhere I've gone, there has been a unanimous answer that I won't be able to get the second phone for the subsidized price until the stated upgrade date. In this case, if you haven't upgraded your phone yet, you might want to wait until the next wave of phones comes out. The RAZR HD is supposed to come out soon. When the RAZR MAXX came out, all the phones in the RAZR line were Buy 1 Get 1 Free. If they do that again, then you both can get new phones without having to worry about the upgrade date for hers.