Option A is the correct answer because "to look after" means to take care of, or to have the attention of, here the wife gave attention to the husband's health and took care of him.
Option B is incorrect because "looked at" means that she was only staring at her husband, as "at" means describing a particular position, here looking at her husband.
Option C is incorrect because "looking for" means that you are searching something, but here the statement talks about the wife taking care of the husband, and not that she was searching for him.
Option D is incorrect because "looked upon" means to judge or regard someone, which means the wife regarded the husband very well, which doesn't make her devoted, as according to the statement she is a devoted wife as he takes care of (looks after) her husband.