First off, I LOVED the episode today. There was so much to it in my opinion. But this part had my laughing so hard. I can't believe Fluttershy did that.
In my mind, BonBon and her friend pretended to just be a bit annoyed but when they parted ways BonBon broke down and ran home to Lyra and told her the news. Lyra wants to be supportive of her friend but is finding the fact that she got her trash dumped all over her by the shyest pony in Ponyville a bit too hilarious. Heh, at least she's trying to be empathetic.