No she didn't, the U.S.A. enacted the War Brides Act in December 1945 which enabled the non asian spouses and children of U.S. service personnel to enter America, but it didn't confer citizenship on them, if they wanted to become U.S. citizens they would have had to apply for that after they arrived in America.
Which is why, if you find an arrival record for her for when she first arrived in America, ( if indeed she did go to America ), you'll probably find that she is listed on an immigration service list and that she is listed as an Australian citizen, ( or as British or whatever nationality she was when she married ).
http://en.wikipedia.org/wiki/War_Brides_Act