Her quasi-experiment [1], which resembles an interrupted time series design [2, 3], does tend to support a causal implication of “living in that apartment”. There seems to be something about living in that apartment that is causing those symptoms. From there, hypothesizing that it could be the air contents doesn’t seem like that much of a stretch to me.

[1] https://sfbayview.com/wp-content/uploads/2021/03/Ashley-Gjov...

[2] https://doi.org/10.1136/bmj.h2750

[3] https://opentextbc.ca/researchmethods/chapter/quasi-experime...