Complex sentence: Minette in particular showed talent for singing, and in 25 December 1780, they were hired at the theatre by Francois Saint-Martin, and in 13 February 1781 she performed in the part of Isabelle in the Opera "Isabelle et Gertrude".
Split into simpler sentences: Minette in particular showed talent for singing, and in 25 December 1780, they were contracted at the theatre by Francois Saint-Martin. In 13 February 1781, Minette performed in the part of Isabelle in the Opera "Isabelle et Gertrude".