请问下列中as起什么作用?Herfacefeltstiffasfrompainandhermouthactuallyhurtfromhavingstretchedit,unwillingly,insmilestopreventthetwinsfromlearninghersecret.为何只有前面一个asfrom,后面都只用from就可以

Question

请问下列中 as 起什么作用?
Her face felt stiff as from pain and her mouth actually hurt from having stretched it,
unwillingly,in smiles to prevent the twins from learning her secret.
为何只有前面一个 as from,后面都只用from就可以了。from不也是有"因为"的意思吗？因为脸部僵硬脸才痛，那另外一句嘴也是因为咧着笑才痛，为何不用as from,而只用from?

Answer 1

as from 是习惯用法,表示：“从…时起”、“从…开始”as 表示“当……时候”
as from pain作状语,意思是：“当疼痛一来的时候”
Her face felt stiff as from pain的意思是：
“他一感到疼痛面部就发僵”
或者：
“疼痛一来,他的面部就发僵.”