So here it’s saying, “Although it seems that she’s by no means thinking of how she will make do [without the other slipper].”
Since the sentence uses an embedded question the “how should~” turns into “how would~” because the narrator isn’t asking for advice but making a comment about what was observed. Additionally since it’s written in present tense, “would” turns to “will”.
The way I interpreted this passage is that Kiki is singing a song with regard to her missing slipper about if she makes do, she’s happy; but if she doesn’t, she isn’t. The narrator points out that Kiki isn’t putting much thought into how to turn this situation around.