When Emily is playing the piece on the piano and Aaron walks into the room, it was in fact Italia Ricci who plays Emily performing the piano concerto and she is credited for it as well.
It's true that this is the intro to Amy Grant's "Sing your Praise to the Lord", but that intro again is Bach's Well Tempered Piano Fugue 2, c-minor, BWV 847. Italia Ricci is playing exactly the first six and a half bars of that Bach piece before being interrupted. The Amy Grant intro departs from the original score in bar 7, and that means Ricci is actually playing Bach.
The piano solo that Italia Ricci's character, Emily Rhodes, plays is the introduction to Amy Grant's version of the Rich Mullins penned, "Sing Your Praise To The Lord," a contemporary Christian music hit from Grant's 1982 album, "Age To Age." Mullins also recorded two of his own versions of the song: the first for the 1981 album, "Behold the Man," and the second--a new recording--for the compilation 'greatest hits' album entitled, "Songs," released in 1996. Amy Grant is a contemporary Christian music artist, as was Rich Mullins until his untimely death in 1997.
This episode takes place in February 2016.