Is it permissible for an eleven-year-old non-Arab girl to limit the last tashahhud to the length of the first tashahhud, without the Salat al-Ibrahimiyyah?

The first Tashahhud is performed without invoking blessings upon the Prophet, peace and blessings be upon him, according to the majority of scholars, and omitting it therein does not invalidate the prayer. As for the last Tashahhud, invoking blessings upon the Prophet, peace and blessings be upon him, is obligatory according to the Shafi'is and Hanbalis. This is achieved by saying "Allahumma salli 'ala Muhammad" (O Allah, send blessings upon Muhammad), and its complete form is the Ibrahimiyyah prayer. If the girl omitted invoking blessings upon the Prophet, peace and blessings be upon him, in the last Tashahhud, then her prayer is not valid according to those who deem it obligatory.