Pelosi doesn't have the votes in the House and Reid, who does not support the AWB, will not push it in the Senate.
For Pelosi to get the votes in the house she would have to strong arm a great deal of her pary members from conservative districts to vote for the legislation which would certainly cost them in the next election. These congressmen know that voting for this would more than likely cost them so I don't know what exactly Pelosi could do to force them to vote their way out of office.
Should Pelosi push for it she knows it will not make it through the Senate so it would be a stupid political move. The republicans have been attempting to use the gun issue, among others, to help them gain back the majority. The safest way for the democrats to prevent them from using the gun issue is to not allow gun legislation to come up for a vote and in the House the majority can make that happen.
We all know what Pelosi's views on guns are and the only thing preventing her from trying to further her views is her desire to remain Speaker.