Ah, alright. Didn't want to spell out her character and be redundant if you had already seen the show.

The joke is her people spent unknown amount of time as seaponies under the sea in hiding, they originally were hippogriffs. Once the threat they were hiding from was dealt with, they returned to land by mixes between the life as seaponies and hippogriffs as the queen granted them the ability to change between the two forms as they pleased, since some had grown a preference for the life under water while others were happy to return to land.



On the show it's a running gag that, after such a long time living under water where stairs ain't a thing because you just swim anywhere, hippogriffs living on land has grown a bit of an excited obsession with stairs. Shown with Silverstream screaming in excitement upon stepping on stairs, even her grown up uncle goes "show me those stairs!" with same excitement.