Like some austrians medias recently announced, should Anna suffer on postnatal depressions. This assumption was activated by her longtime friend and director of "La Bohème" Robert Dornhelm, because of his evidence at the premiere "What Anna now needs desperately is time and calmness together with her family". This should be the reason for not coming to the premiere on 8th october.
I don't know if this information is right or only a myth by the medias, but if it is the truth I can only wish her all the best and enough power to get of it.
Thanks to Lisa for the information