@Zyr87  
Flutterbat is to Fluttershy what Hulk is to Banner. If that’s not a persona, I don’t know what to call it.

Well (and I may be overthinking this, but):
 
Flutterrage wasn’t a persona so much as just sanity slippage.  
Flutterbat was magic gone wrong, not her fault, nor really a persona.  
Rainbow Powered shy was just a power upgrade, no real personality change.  
Discorded Shy was something that all the mane six fell victim to (and Flutters was the only one who had to be forced to become evil, the rest were tricked quite easily).  
Saddle Rager, again, had no real personality change (in fact, it took some serious work to make her rage, IIRC).
 
A case could be made for assertiveshy (or flutterbitch if you’d prefer) as well as her three personas in Fake It Til You Make It, though. In the first, she went way too far with assertiveness training, and in the second, she got lost in character, becoming three new personas.

She was best Celestia impersonator in Testing 1, 2, 3
 
She’s still the best impersonator now!

@Background Pony #1EFB
 
@Lord Seraph  
Or like the (Persona game protagonist) of the six.

Fluttershy is really the Ditto of the six.

@FamusJamus  
Don’t forget the three new additions from Fake It ’Till You Make It.
 
Wow, Fluttershy has a LOT of personas now.

@Background Pony #98A4  
She really needs an intervention.  

Stay in your own form, Fluttershy.