Does a sin or an effect on the validity of the prayer result for one who was ignorant of the obligation to recite the first Tashahhud in the last Tashahhud and sufficed with the Salatul Ibrahimiya?

The preponderant opinion is that the final Tashahhud (definition) is a pillar of prayer. The questioner must, therefore, make up the prayers she performed without it, because omitting a pillar invalidates the prayer. Ignorance does not waive the obligation of making up prayers, according to the majority of scholars. If she is unaware of the number of prayers, she must continue to make them up until she is reasonably certain that her obligation has been fulfilled. There are other opinions that hold that making up prayers is not obligatory for the ignorant, or that the final Tashahhud is not a pillar.