If gensokyo or its inhabitants were that fragile it would have collapsed at its first incident. Sounds more like she's trying to validate keeping Cirno around as a her personal AC.
Guedez said: toss cirno in a vulcano, guess what happens. Also, go ask Shikieiki
Over the course of a year the volcano becomes a frozen mountaintop. At the end of said year, a pissed Cirno come out.
You nearly collapsed after leaving your chilly lake, right?...heh.And what then?It won't do if either fairies or youkai disappear.If you were to disappear, Letty wouldn't be able to live either.It wouldn't be appreciated if balance in Gensokyo crumbled because of just one selfish fairy."She wanted to see Letty so badly that she pushed herself too much and died." That wouldn't even go for a joke.And that goes not only for supernatural beings. All life in Gensokyo bases itself on mutually coexisting beings.