The way it stands now,as long as there are male heirs,Alexandra is not going to inherit the throne( a form of Salic law of agnatic primogeniture).His Royal Highness Hereditary Grand Duke Guillaume Jean Joseph Marie of Luxembourg, the Grand Duke's eldest son, born on November 11, 1981. He is the Hereditary Grand Duke of Luxembourg, Hereditary Prince of Nassau and holds the title Prince of Bourbon-Parma. His brother, Prince Louis,renounced his right to the throne;any children of his will hold the surname de Nassau with no titles.His Royal Highness Prince Sébastien Henri Marie Guillaume of Luxembourg, born on April 16, 1992,although younger than Alexandra(born 1991),would be the next male heir in line.Alexandra would be next in line,but if the brothers have children,they go in front of her in line of succession.
This is the current line:
HRH Hereditary Grand Duke Guillaume, eldest son of the Grand Duke, born 1981
HRH Prince Félix, second son of the Grand Duke, born 1984
HRH Prince Sébastien, fourth son of the Grand Duke, born 1992
HRH Princess Alexandra, only daughter of the Grand Duke, born 1991
HRH Prince Guillaume, brother of the Grand Duke, born 1963
HRH Prince Paul Louis, son of Prince Guillaume, born 1998
HRH Prince Léopold, son of Prince Guillaume, born 2000
HRH Prince Jean, son of Prince Guillaume, born 2004
ANd the current Salic Law that Luxembourg follows,according to wikipedia is
"The constitution of Luxemburg states that the crown is hereditary in the house of Nassau according to the pact of 1783 (the Nassau Family Pact), the Treaty of Vienna made in 1815, and the Treaty of London (1867).
In April 1907 William IV, Grand Duke of Luxembourg decreed (approved in July 1907 by legislature of Luxembourg and thereafter enacted) amendments to the House law of Nassau: the Grand Duke's eldest daughter will succeed (that provision is identical with the effect of the 1783 pact), and after her, her issue in male line born of marriages that abide by the house laws; in default thereof, the Grand Duke's next daughters in similar fashion. Thus, issue of the Grand Duke's daughters received succession rights only in strict agnatic line - a male-line male descendant of a younger daughter will (presumably) have preference over female descendants of elder daughters. (Conceptually, this is not the so-called Semi-Salic principle, since in that system, upon extinction of one daughter's male-line issue, the closest heir of the last one of that line succeeds, which means first a descendant in female line of that daughter and not yet descent from younger daughters.) The current law of succession in Luxemburg follows a special order among male lines issued from Grand Duke Guillaume IV's daughters.
The present law of succession is effectively the law of July 1907. It was never passed as an amendment to the Constitution, but as a regular law. The constitution of Luxembourg still stipulates only that the crown is inherited according to the pact of 1783, the 1815 treaty, and the 1867 treaty of London.
The position of husband is null in constitutional terms from that 1907 decree onwards (identical with the position of wife of a male Grand Duke), as a marked contrast to medieval practice, where the husband reigned in his wife's right.
Accordingly, Felix of Bourbon-Parma, the husband of the second reigning Grand Duchess, received position and titles of effectively of that of prince consort.
The law of July 1907 reserves for the Grand Duke the right to unilaterally amend the house laws. It has been reported that Jean, Grand Duke of Luxembourg so enacted at least twice. Those amendments have not been published."