Did we ever find out what Fluttershy's song was?

[Note Wise 30]

I know that throughout the movie the running joke is that Fluttershy wrote a song, yet they won't play it. It seems like a wasted joke and went nowhere...but I have a feeling the final song, "Shine like Rainbows." was the song she wrote for the band.

[PROJECT: Simon 3,953]

Yeah... I think it played it in Rainbow Rocks, the final song. If I'm wrong, please correct me. 

Edited March 4, 2015 by Simon the Salem

[StormRider245 61]

I am not quite sure, but I suppose it was the song Fluttershy was writing. Because it fits and seems logical.

[That One Pone 584]

To be honest, I have a feeling that the second half of "Welcome to the Show" may have been what was referred to, otherwise as you guys say above, probably "Shine like Rainbows"

[Moonlight 7,279]

Right before they go out to fight the Dazzlings, they decided to choose Fluttershy's song to play, so it can be assumed that the Rainbooms part in "Welcome to the Show" is her song.

 

"It doesn't matter what song we play, as long as play it together, as friends!"

 

"Fluttershy's written a really great one."

 

And they then go out to sing. 

[Will Guide 21,325]

Exactly! In fact, the first lyrics the Rainbooms sing are "I got the music in me!" is nice nod to Season 4's Fluttershy episode, Filli Vanilli, where her favorite quartet, the PonyTones sing a similar song with similar lyrics! 

 

Although, when Sunset finally sings her lyrics... "You're never going to bring me down/ you're never going to break this part of me/ My friends are here to bring me around/ Not singing just for popularity!" I kept wondering, "Were those Sunset's own words, or were those really Fluttershy's lyrics that heart-warmingly and coincidentally have more meaning when sung by Sunset?" I choose the latter.

[Sidral Mundet 1,666]

I think the first half of the Rainboom's song during the Welcome to the Show song was written by Fluttershy.  The part where Sunset Shimmer is singing I'm not as confident about. For all I know Sunset could have adlibed it there.