WLNI-MLYNCHBURG, Va. (AP) _ A former Roanoke woman has pleaded guilty in a Smith Mountain Lake mortgage fraud scheme.   Susanne Helbig, who now lives in Georgia, was charged in a 15-count indictment in May. She pleaded guilty to one count of mortgage fraud conspiracy and one count of tax fraud Thursday in U.S. District Court in Roanoke. Media outlets report that the other 13 counts were dismissed. The indictment claimed that in 2006 and 2007, Helbig and others submitted false and fraudulent mortgage loan applications and settlement statements in the name of straw purchasers. The losses were calculated at about $11 million. The 50-year-old Helbig will be sentenced Jan. 20.