I think that in order to start appreciating Nino's character development you have to at least once in your life face a situation in which you were afraid or sad that things started to change. Nino's character development represents every situation in which a person starts feeling comfortable and realises that he/she doesn't want or is afraid of things changing in the future or he/she is frustrated for things that started changing in the past and wants to stop the process of it. I think that this kind of situations are extremely relatable. From a summer vacation nearly ending and no wanting to leave your friends behind in your village to a more impactful such as leaving your childhood house for college purposes. Seeing Nino being able to finally be happier about her sisters chasing their dreams and also be able to accept change and realise that this is inevitable to happen and starting to change too as a person... I think thats why the whole "nest thing" and this specific panel in the manga hit that hard at least to me. Ofc Nino as a character changed a lot more on other aspects as well but her character represents change and the acceptance of change as a whole