Spoilers for Season 7:

You didn’t honestly believe that, did you?

In part 1, Twilight found out that Fluttershy’s into diapers as well. Now they’re getting together for their first padded slumber party…

I got this from channel surfing across parallel universes. It’s pretty dank. Wish I would’ve seen part 1.

Alternatively,

In part 1 she suffered something terrible, and lost control of some of her bodily functions. She’s excited to show off to Fluttershy that she’s regained a little bit of control, meaning she’s using pullups now instead of tape-on diapers!

Also, have no fear, pullups that can take a good 3-4 moderate wets or 2 soaks do exist. And maybe in Equesrtia there’s ones as good as tapes…