Sleep well, Glimmy.

“You don’t understand me, music box mom!”

@when she felt her wings unfold  
Like teacher like student.

@Princess Trixie vi Equestria  
I would guess that Celestia gave her VIP guests a choice of rooms they could stay in for the night.  
Starlight probably prefers simplicity over extravagance as a contrast to Rarity’s preference. Either that, or that was the only suitable suite available at the moment.  
You could also keep in mind that the castle was also hosting mayors and officials from other parts of Equestria during the time of the episode. Hence the town hall meetings.

@SeraphimDawn  
The one thing I keep on wondering though is why the hell are the princesses so damn cheap on giving Starlight a decent bedroom or at very least a decent bed?
 
What do they have against her having quality sleep on a king size bed, I mean okay I get that Twilight didn’t want to spoil Starlight so she gave her a more humble bedroom and bed to live at her castle but while visiting Celestia and Luna there certainly was no reason for the two royal sisters to cheap up on where they let Starlight sleep.
 
Was it favoritism for mane6 or they simply dislike Starlight? they kept giving her a single size small standard bed… On comparison look at the bed Princess Celestia provided Rarity when she was staying at the castle at Twilight’s request:
 

 
Oh Rarity wins a noble-pony bedroom and bed, but Starlight meh give her the maid bedroom.

@Princess Trixie vi Equestria  
That is something I’ve noticed.
 
In almost every episode she appears in, there are scenes of her in her bedroom on her bed.  
I think she has appeared in bed more than most other Mane 6 ponies by this point.

You can’t have a nightmare if you never dream.

So every Starlight new episode we’ll see her at bed? is this “fan service” to us cloppers? xD

Mornings.