Questions & Answers about Siostra stoi na drabinie i maluje sufit nową farbą.
Siostra is the subject of the sentence, so it appears in the nominative case.
Basic dictionary form:
- siostra = sister
In this sentence, siostra is the person doing the actions:
- stoi = is standing
- maluje = is painting
So Polish uses the nominative form siostra.
Polish often uses specific verbs for physical position instead of just to be.
- stać / stoi = to stand / is standing
- siedzieć / siedzi = to sit / is sitting
- leżeć / leży = to lie / is lying
So Siostra stoi na drabinie means The sister is standing on a ladder, not just The sister is on a ladder.
This is very natural in Polish.