I'm not sure exactly what happened. Taylor Swift may just have been too busy with recording or touring or the producers finally decided she wasn't quite going to cut it. Anyway, I don't really care why, like I said before, I am just so glad they chose Samantha. Samantha has played Eponine in the stage production of Les Miserables as well as in the 25th anniversary concert that took place in 2010.
Here is Samantha singing On My Own.